Dizziness is a common side effect of Prazocel (prazosin), especially after the first few doses or if your dose has been increased. This happens because the medicine lowers blood pressure, which can cause light-headedness or fainting. If you feel dizzy, sit or lie down immediately and avoid standing up quickly. Do not drive or operate machinery until you feel normal. Drink enough fluids and rise slowly from sitting or lying positions. If the dizziness is severe, persists for a long time, or is accompanied by fainting, chest pain, or confusion, contact your doctor right away, as your dose may need to be adjusted.