Dizziness often occurs when a person squats for a long period and suddenly stands up. When you stand for a long period, blood can pool (due to gravity) in the legs which can deprive the brain of a level of oxygen and nutrients, so that gravity no longer pulls the blood to the legs. Dizziness might occur when getting up fast from lying down. Because the blood is unable to reach the brain readily, your heart is unable to pump it there fast enough, your brain is again temporarily deprived of O2 and needs to equilibrate, which is called postural or orthostatic hypotension.
Examples of Vertigo
With vertigo, a person feels like a world is spinning despite laying still. These symptoms are differentiated by the motion that continues once a person is sitting, lying or standing still.