Sitting without dizziness and lying down with dizziness may be caused by benign positional vertigo, cervical spondylosis, cerebral atherosclerosis and other reasons. 1. Benign positional vertigo: when the human body suddenly lies down from the sitting position, due to the change of head position, it is likely to cause otoliths to fall off, when the otoliths fall off to the semicircular canals, and when the stimulation is formed on the local cell membranes, it will cause dizziness, which will show the symptom of dizziness when sitting without dizziness and lying down. 2. Cervical spondylosis: commonly seen in vertebral artery type cervical spondylosis, this kind of patients in lying down easily lead to intervertebral disc compression of the vertebral artery, affecting vertebral artery blood circulation, resulting in insufficient blood supply to the brain, which will cause dizziness. Thus, it shows the symptom of dizziness when sitting or lying down. 3. Cerebral atherosclerosis: patients with this disease have narrowed blood vessel lumen and thickened blood vessel wall, which leads to slow blood flow and causes insufficient blood supply and oxygenation of brain tissue, and lying down will lead to slow blood flow and aggravate insufficient blood supply to the brain, which will aggravate the symptoms of dizziness. Therefore, it will show the symptoms of dizziness lying down without feeling dizzy. Sitting without dizziness lying down dizziness, may also be caused by other reasons, if the symptoms frequently recurring, should be as early as possible to seek medical attention, through the improvement of the relevant examination, diagnosis of triggers, to give targeted treatment.