Head dizziness and unsteadiness when standing up may be caused by the following reasons: 1. Physiological reasons, head dizziness and unsteadiness are caused by the sudden standing and rising of blood concentrated in the distal end of the body, which leads to a shortage of blood supply to the brain when standing up, thus causing the symptoms of head dizziness and unsteadiness. 2. Pathological factors, including stroke, cerebral infarction and other diseases. The vestibular disorder of the inner ear or ophthalmological disease may cause sudden head dizziness and unsteadiness when standing up.