Fainting may be the sign of a serious problem and a need for immediate medical attention if it happens often in a short period of time and without warning; when pregnant, it causes confusion, trouble talking, blurred vision; if you are losing a lot of blood or feel short of breath; you have chest pain, irregular heart beating and it happens along with numbness or tingling on one side of the face or body; if fainting more than once a month or taking longer than a few seconds to regain consciousness.
Attribution: Straight Talk Foundation