Fainting, also known as syncope, is a temporary loss of consciousness that is usually caused by a temporary drop in blood flow to the brain. It can be caused by a variety of factors, such as dehydration, low blood sugar, heart problems, or sudden changes in posture. Fainting can also be a side effect of certain medications or a symptom of an underlying medical condition. Symptoms that often precede a fainting episode include dizziness, lightheadedness, nausea, and sweating. After fainting, a person may feel confused, weak, or nauseous for a few minutes or longer. Fainting can sometimes indicate a serious medical condition and should be evaluated by a healthcare professional if it occurs frequently or is accompanied by other symptoms.