Hello dear, I understand your concerns.You are probably having syncope episodes. Syncope is a very short episode(often seconds to a minute) of excessive sweating,palpitations,dizziness,lightheadedness,blurred vision or transient loss of consciousness, when a person is in erect posture or mostly when he/she stands from the sitting posture.It is due to decreased blood perfusion to the brain for few seconds after which body adapts.It improves if patient is made to lie down, as lying down increases the blood supply to the brain.You need to get your blood pressure checked in lying as well as standing posture to see if there is a significant drop in standing posture.Further, please visit a neurologist,so that he may investigate you accordingly.I hope it helps you.