Dizziness is caused when the head is tilted to one side and is mainly seen in two diseases: benign positional vertigo and cervical spondylosis. Benign positional vertigo can induce transient dizziness when the head moves to a fixed position for a few seconds or tens of seconds, and it occurs mostly in the elderly. Cervical spondylosis can also cause dizziness with the head turned to one side, and angiography is needed to see if it is caused by cervical spondylosis. When the head is in a neutral position, the angiogram is normal, but when the head is turned, the angiogram shows that the blood flow is interrupted. The blood flow in the vertebral artery and the posterior cerebral artery is monitored by transcranial Doppler ultrasound, and the blood flow is normal before the head is turned, but after the head is turned, the blood flow is interrupted, and the blood flow is restored when the head is returned to a neutral position.