Hi, Thank you for writing in, You report symptoms of dizziness or head spinning mainly when you stand up from a sitting or lying down position from the past 2 days. If it occurs only with a change in posture then it is more likely that it is a postural drop in blood pressure that is causing it. And yes, loss of fluids in the body or dehydration due to excessive sweating and inadequate intake of water can cause it. Vertigo is a symptom that can be caused by either peripheral causes related to the inner ear or central cause involving the brain. An evaluation by a physician will clear your doubts. Hope this helps, Dr A Rao