Fainting and Low Blood Pressure: When to Go

Key takeaways

Most faints are harmless, but one group comes from the heart. What separates the two is the CIRCUMSTANCE of the faint, not the number on a home blood-pressure machine.
According to NHS, fainting DURING EXERTION, fainting WHILE LYING DOWN, fainting with chest pain or a pounding, erratic heartbeat, and fainting with injury are all reasons to call the emergency services.
By contrast, an episode with warning signs — light-headedness, vision greying out, a cold sweat, nausea — that happens after standing a long time, in the heat, in pain or in fright, and is followed by a complete recovery, is usually harmless.
The right thing to do for someone about to faint, or who has just fainted, is to LIE THEM DOWN and RAISE THE LEGS, and loosen the collar. Do not hold them upright, do not tip them head-down, and do not pour anything into their mouth.
Not coming round quickly, or not breathing normally: that is a different situation altogether from a faint — call 115 and follow the chest-compression instructions.
According to NHS, anyone who has fainted should see a doctor even after a full recovery. If light-headedness is new since a change of medicine, have a doctor or a pharmacist go back through the prescription — do not stop the medicine yourself.

Most faints are harmless: standing a long time, standing up too fast, being in pain or in fright, then passing out briefly and coming round completely. But one group of faints comes from the heart, and that group is dangerous. What separates them is the CIRCUMSTANCE of the faint, not the number on a home machine.

Recognising it: what the person was doing when they fainted

Three questions decide more than any home reading: what were they doing at the time, did they get any warning before they went down, and did they come round quickly and completely. The harmless group:

They were STANDING: standing still a long while, or had just got up from bed or from a chair.
There is a clear setting: hot weather, being in pain, being frightened, having just seen blood.
There were WARNING SIGNS: light-headedness, vision greying out, a cold sweat, nausea, sounds seeming to recede.
They came round QUICKLY AND COMPLETELY: they know where they are, and speak and move normally.

According to CDC, heat-related light-headedness and fainting usually happen after standing too long or after standing up suddenly from sitting or lying. According to MedlinePlus, hard coughing, straining on the toilet and passing urine at night can also cause fainting.

The group to worry about differs in the circumstance itself — according to NHS, fainting during exercise or while lying down is already a reason to call the emergency services; the full list is in the box below.

What it is mistaken for

CARDIAC ARREST is the most expensive mistake. According to MedlinePlus, the first sign of sudden cardiac arrest is often loss of consciousness itself. The difference: someone who has fainted comes round, someone in cardiac arrest does not and is not breathing normally — that is the moment for chest compressions, not for raising the legs.

What to do straight away

Someone who is light-headed and about to go down: get them SITTING or LYING where they are. Do not hold them upright and do not walk them along — falling while light-headed is the commonest complication of all.
Someone who has already gone down: according to NHS, shake the shoulders GENTLY and call out loudly, then check whether they are breathing normally. If they are, lay them on their back, RAISE BOTH LEGS, and loosen the collar.
If they vomit, lay them on their side so they do not choke. From 28 weeks of pregnancy, NHS advises lying on the side.
Keep them lying down for another 10 to 15 minutes somewhere cool and quiet, as MedlinePlus advises, before letting them sit up slowly. In hot weather, CDC advises getting them into the cool; give sips of water only once they are fully awake.
Write it down: what they were doing, whether there was any warning, whether there was jerking or loss of bladder control, and what medicines they take.

What must NOT be done

Do NOT squeeze lime juice, pour water, or give anything by mouth to someone who is not fully awake — the swallowing reflex is not safe at that point and the liquid goes into the lungs.
Do NOT hold them upright or make them walk about “to bring them round” — standing them up is the way to make the faint repeat immediately.
Do NOT tip them head-down, shake them by the shoulders hard, slap them, press the point under the nose, scrape the skin with a coin, or prick the fingertips for blood — NHS advises only shaking the shoulders GENTLY and calling out loudly.
Do NOT make a home blood-pressure reading the basis for calling the emergency services — not one of the signs in the red-flag box is defined by a blood-pressure number.
Do NOT take extra doses of, or stop, blood-pressure or heart medicines on your own after a faint. Do not carry someone who has just fainted on a motorbike.

Light-headedness on standing, and the question of medicines

According to NHS, light-headedness that appears only on standing up or changing position is a sign of postural low blood pressure: get up slowly — lying to sitting, sit for a moment, and only then stand — and avoid standing still in one place for too long.

The medicines are where the most can be put right. MedlinePlus lists some medicines for anxiety, depression and high blood pressure among the causes of fainting; NHS says that if a medicine is the cause, a doctor may change it or adjust the dose. So take the boxes with you to the appointment and have a doctor or a pharmacist go back through the prescription — do not stop anything yourself. The part about preventing falls in older people is covered in the article on dizziness.

When you must go to hospital

CALL 115 (the emergency number in Vietnam) NOW if someone who has just fainted: is not breathing, or is only gasping — follow the chest-compression instructions from the dispatcher · does not come round quickly when shaken and called · has come round but is not back to normal: difficulty speaking, not understanding what others say, weakness or numbness of one arm or leg, one side of the face drooping, blurred vision, confusion · has chest pain or heaviness, a pounding or erratic heartbeat · has a seizure, or stiffening of the arms and legs · has been injured by the faint: a blow to the head, bleeding, a fall from a height · has bitten the tongue, or lost control of bladder or bowel. Also call the emergency services if the faint happened DURING EXERTION or WHILE LYING DOWN; and, according to MedlinePlus, if the person who fainted is pregnant, over 50, or has diabetes. — BE SEEN WITHIN 24–72 HOURS, even after a full recovery, if: this is a first faint; the faints are recurring; there are new symptoms alongside the faint; light-headedness or fainting is new since a change of medicine or a dose increase; the person has heart disease, or the family has had sudden cardiac arrest in someone young. According to NHS, anyone who has fainted should see a doctor.

What can be done at home, and when to go in

Put plainly: the cause of a faint cannot be found at home — separating a cardiac faint from a harmless one needs heart-rhythm monitoring and tests.

If you are not sure whether you need to go in, start with a remote consultation by video call. At home, a doctor takes the history, examines at the bedside, measures the blood pressure lying and standing, goes back through the prescription, and then says clearly whether this case is watched further or has to go in. After discharge, a nurse comes to the house for recovery care. A remote consultation is not for anyone drowsy or having seizures — with a sign in the box above, go in first and call afterwards.

Sources: NHS in England (fainting, low blood pressure) and MedlinePlus at the US National Library of Medicine (fainting, cardiac arrest). The US CDC has no general-public page on fainting or low blood pressure, so only the part about heat-related light-headedness and fainting follows CDC. This article passes that on and does not replace being examined; citing CDC here does not imply that CDC endorses Y Te Xanh or our services.

Need personalised advice for your loved one? Call our hotline 094 368 81 15 (24/7) — calling to ask a question or to book costs nothing. GreenCare has doctors who come to examine, nurses who carry out doctor's orders (injections, infusions, dressing changes), remote consultation by video call, and a review of the medicines you are taking; an in-depth remote consultation, or any one after the first, is a paid service. For children we take examination and acute care only — not long-term care at home, and not newborns or expectant mothers. We confirm we have staff in your area and provide transparent pricing before we begin.

Sources

NHS — Fainting
NHS — Low blood pressure (hypotension)

Frequently asked questions

How low does blood pressure have to be to count as low and to need emergency care?

NHS does have a reference point for NAMING the condition of low blood pressure, but this article deliberately does not print that number, because it is not the condition for calling the emergency services. Read the red-flag box again: not one of the signs there is defined by a blood-pressure number. Someone with a low reading and no symptoms is in a completely different position from someone who fainted while running with a reading that looks normal — and it is the second person who needs emergency care. Home readings are still useful: write them down and take them to the appointment, but do not use them to decide for yourself whether to go.

If someone is about to faint, should they be sat down or laid down?

Lay them down, and raise both legs. According to NHS, when a person has fainted and is still breathing normally, lay them on their back and lift the legs; MedlinePlus advises raising the feet above the level of the heart, loosening tight clothing around the neck, and then keeping the person lying down for a while somewhere cool and quiet. Someone who has not gone down and is only light-headed can be sat or laid down where they are — the important thing is not to hold them upright and not to walk them along, because falling while light-headed is the commonest complication of all.

Is squeezing lime juice into the mouth of someone who has fainted the right thing to do?

No. The swallowing reflex is not safe in someone who is not fully awake, so lime juice, sugar water or medicine poured into the mouth can run into the lungs — one more illness on the way to hospital. In the same group: tipping them head-down, slapping them, shaking the shoulders hard, pressing the point under the nose, scraping the skin with a coin, pricking the fingertips for blood. None of those raises blood pressure. What helps is lying them down, raising the legs, loosening the collar, and checking whether they are breathing normally.

Is fainting while playing sport different from fainting after standing a long time?

Entirely different, and this is the most important point in the article. According to NHS, fainting while exercising is one of the reasons to call the emergency services, along with fainting while lying down and fainting with chest pain or a pounding, erratic heartbeat. By contrast, passing out after standing a long time in the heat, with warning signs beforehand and a prompt recovery, is usually harmless. Young, fit people are most often overlooked in exactly the first case: they explain it to themselves as having overdone it, and carry on playing.

Light-headedness started after a change of medicine — should I stop the medicine myself?

Do not stop it yourself, particularly blood-pressure, heart or diabetes medicines — stopping can be more dangerous than the light-headedness. MedlinePlus lists some medicines for anxiety, depression and high blood pressure among the causes of fainting, and NHS says that if a medicine is the cause, a doctor may change it or adjust the dose. What you should do is write down what you are taking, bring the boxes, note the time you take them and the time the light-headedness starts, and have a doctor or a pharmacist go back through the prescription. If there is also fainting, chest heaviness or an erratic heartbeat, go now rather than waiting for an appointment.

If the recovery was complete, is there still any point in being seen?

There is. According to NHS, anyone who has fainted should see a doctor; MedlinePlus puts it more precisely — even when it is not an emergency, be seen soon if this is your first faint, if the faints have been recurring, or if there were new symptoms alongside this one. The reason is that a quick recovery does not rule out a cause in the heart, and that cause needs equipment to see. With none of the signs in the red-flag box, being seen within one to three days is reasonable; with one of them, go now.