What can cause light headedness or being dizzy when i stand up and what should i do for this?

Lightheadedness: As described is highly suggestive of orthostatic hypotension, typically caused by drugs and/or mild dehydration. You should let your doc know as well so that you can see him or her to start diagnostic workup. Your symptoms will make you prone to falls and any transition from sitting or laying to standing should be slow in order to allow for your blood pressure to increase.