My left hand becomes numb when I lie down, but it's fine when I sit up.

　　Numbness in the right hand when lying down, which disappears upon sitting up, may be caused by physiological factors or pathological conditions such as insufficient cerebral blood supply or cervical spondylosis. Symptoms can be improved through general treatments, medications, and other approaches. Specific analyses are as follows:

　　I. Physiological Factors

　　If a patient maintains an improper sleeping posture while lying down, it may compress the nerves and blood vessels in the right hand, leading to numbness. This is a normal physiological phenomenon and typically does not require special treatment if no other discomfort symptoms are present.

　　II. Pathological Factors

　　1. Insufficient Cerebral Blood Supply

　　Insufficient cerebral blood supply is usually caused by narrowing or blockage of cerebral blood vessels due to various reasons, resulting in brain hypoxia and ischemia. When lying down, vascular obstruction may worsen and blood flow slows down, thereby causing numbness in the hand. Patients may take medications such as Naoxintong capsules, Danshen dripping pills, or enteric-coated aspirin tablets as directed by a physician to improve symptoms.

　　2. Cervical Spondylosis

　　Patients who already have cervical spondylosis, such as lumbar disc herniation or lumbar muscle strain, may experience compression of nerve roots when lying down, leading to hand numbness. Treatment may include medications such as mecobalamin tablets or eperisone hydrochloride tablets.

　　In addition to the above causes, hand numbness could also result from conditions such as dorsal scapular nerve entrapment, carpal tunnel syndrome, or diabetic complications. Patients should seek symptomatic treatment under the guidance of a doctor according to their specific condition.