Lying down is fine and getting dizzy as soon as you get up may be postural hypotension, which is also seen in people who usually have low blood pressure and are physically weak. Postural hypotension is a systemic autonomic dysfunction disorder. Usually patients have higher blood pressure in the recumbent position and lower blood pressure in the upright and seated positions. When standing up suddenly from the recumbent position, it may cause a transient drop in blood pressure, which may easily cause cerebral hypoperfusion and may lead to insufficient blood supply to the brain, including insufficient blood supply to the cerebellar brainstem and insufficient blood supply to the brain. Insufficient blood supply to the cerebellar brainstem makes patients mainly present with dizziness, nausea and vomiting, balance disorders and ataxia, and also nystagmus and diplopia. Insufficient blood supply to the cerebral brain causes patients to mainly present with blackness in front of the eyes, and may also present with limb sensory impairment, motor impairment, and may also present with hemianopia.