Fainting: Common Causes, What to Do, and When Passing Out Is Serious
Most fainting is a harmless, brief drop in blood flow to the brain. Here's what causes it, what to do in the moment, and the signs that make fainting an emergency.
Fainting (syncope) is a brief loss of consciousness from a short drop in blood flow to the brain, and most people come around within a minute. The most common kind, vasovagal fainting, is set off by things like standing a long time, heat, pain, the sight of blood, or getting a shot, and it's usually harmless. Fainting during exercise, while lying down, with chest pain or a racing heart, or after a head injury can mean a heart or other serious problem: call 911.
Common causes
- Vasovagal fainting: triggered by heat, standing for a long time, pain, fear, the sight of blood, needles, or straining. Often there's warning: lightheadedness, nausea, sweating, tunnel vision or feeling hot.
- Standing up too fast, especially when dehydrated. Our post on feeling dizzy when standing up covers this.
- Dehydration, from heat, illness, exercise or altitude
- Low blood sugar
- Medicines that lower blood pressure
- Heart rhythm problems or other heart conditions, which are less common but more serious
What to do if someone faints
- Lay them flat on their back and raise their legs about 12 inches
- Loosen tight clothing
- Check that they're breathing
- If they don't come around within a minute, call 911
- When they wake, have them stay lying down for 10 to 15 minutes, then sit up slowly
- If they're not breathing, call 911 and start CPR
If you feel faint
Sit or lie down right away, with your head low or legs raised, so you don't fall. Crossing your legs and tensing your muscles can help. Sip water and have something to eat once you feel better.
What urgent care can do
After a simple faint with a clear trigger, a clinician can check your blood pressure lying and standing, check your blood sugar, do an EKG to look at your heart rhythm, and check for dehydration or injuries from the fall. If anything points to a heart problem, you'll be sent to the ER.
At an AfterOurs clinic, a standard self-pay visit is $175, a visit with one moderate service such as an EKG is $250, and a self-pay in-clinic visit never costs more than $330. We contract with all major commercial and government plans, including Colorado Medicaid and Medicare. See the cost and insurance page.
Call 911 if someone doesn't wake up within a minute, faints during exercise or while lying down, has chest pain, a racing or irregular heartbeat or shortness of breath, has a seizure, is confused or has trouble speaking or weakness afterward, hit their head, is pregnant, is over 50 and fainted for the first time, or has a heart condition or family history of sudden death.
Where to find us
Four clinics across metro Denver, all ages welcome, se habla español:
- Hampden (Southeast Denver): 8 AM–11 PM daily
- Littleton: 8 AM–11 PM daily
- Thornton: 8 AM–11 PM daily
- Highlands: Mon–Fri 5–11 PM, Sat–Sun 8 AM–11 PM
Walk in, or book online.
Medically reviewed by Peter Martinuzzi, MD
This article is general health information, not medical advice for your situation. If you are worried, come in or book a telehealth visit — and if it is an emergency, call 911.