There are two causes of syncope that can be due to the heart and blood vessels. The first is due to a rhythm abnormality, such as the heart rate being two slow or too fast. The other cause is due to irregularities in the involuntary (autonomic) nervous system causing low blood pressure, low flow to the brain, and fainting. Syncope, or loss of consciousness, is the body’s normal response to low blood pressure, causing you to fall to the ground and allowing the blood which may be pooled in your legs or abdominal organs to return to the heart, raising the blood pressure and returning you to consciousness. Because of this, lying down is an effective means of both preventing syncope and treating it when it occurs.
The common, benign form of syncope has the medical name of neurally mediated syncope; however, your doctor may have used one of many other names including neurocardiogenic, vasovagal, vasodepressor, or a simple faint. All of these names refer to the same problem.
The typical mechanism for neurally mediated syncope is an inappropriate relaxation of the blood vessels and lowering of the heart rate, leading to low blood pressure at a time when the body actually needs constriction of the blood vessels and a slightly higher heart rate. These inappropriate changes in the heart and blood vessels are due to an irregularity in the control of the autonomic (involuntary) nerves which carry signals from the heart and blood vessels to the brain and back to the heart and blood vessels.
In some way we do not understand completely, the brain’s control of these involuntary signals gets confused and withholds the activity of the sympathetic autonomic nerves which release adrenaline, when it should be activating them. The result is the process which leads to low blood pressure described above.