I am a guy in early 20ies.some times when i stand up (after sitting or laying down on bed) i feel dizziness.it also happens sometimes when i stand straight on weighing machine after exercise.please help how can i stop feeling dizziness?

your description suggests orthostatic hypotension which means a fall in blood pressure in the upright position. Dehydration, medications, autonomic disorders may all cause this. You should be evaluated by your physician to confirm your observation with a BP recording and if confirmed he/she can do further testing to determine the cause. Please do this as soon as you can.

If these symptoms are new they could indicate Blood Pressure drop in the upright position or with change in posture. BP check in the sitting, lying down and standing positions should be done along with a complete physical and appropriate laboratory evaluation. The PCP is the one to begin the clinical assessment with eventual resolution. So see PCP.