Vasovagal syncope is one of the most common causes of fainting. In this situation, the balance between the chemicals adrenaline and acetylcholine is disrupted. Adrenaline stimulates the body, including making the heart beat faster and blood vessels narrower. Acetylcholine does the opposite. When the vagus nerve is stimulated, excess acetylcholine is released, the heart rate slows and the blood vessels dilate, making it harder for blood to defeat gravity and be pumped to the brain. This temporary decrease in blood flow to the brain causes the syncopal (fainting) episode.

Pain can stimulate the vagus nerve and is a common cause of vasovagal syncope. Other noxious stimuli can do the same thing, including a situational stressor. It is common for medical and nursing students to faint when observing their first operation or autopsy. Some people pass out when they hear bad news; others pass-out when they experience the sight of blood or needles.

Other situations commonly cause the heart rate to temporarily slow and cause a faint. Straining with urination, bowel movement, or coughing can cause a vagal response.

Initial laboratory tests may include an electrocardiogram (EKG) and screening blood tests like a complete blood count (CBC), electrolytes, glucose, and kidney function tests. Thyroid blood tests may be performed.

You can take immediate treatment steps when someone has fainted:

* Check the person's airway and breathing. If necessary, call 911 and begin rescue breathing and CPR.
* Loosen tight clothing around the neck.
* Keep the person lying down for at least 10 - 15 minutes, preferably in a cool and quiet space. If this is not possible, sit the person forward and place their head between their knees.
* If vomiting has occurred, turn the person onto their side to prevent choking.
* Raise the person's feet above the level of the heart (about 12 inches).