There are several reasons for one leg numbness when sleeping: 1, due to sciatic nerve compression, caused by sciatic nerve compression for many reasons, such as sleeping due to incorrect posture will make the lumbar sciatic nerve is compressed, which will appear leg numbness this situation. If there is a lumbar spine disease and sciatic nerve root compression phenomenon, the symptoms may be aggravated when sleeping, there will also be a leg numbness. 2, due to lower limb vascular occlusion, people in sleep due to slow blood flow will lead to lower limb artery occlusion, once the lower limb artery thrombosis will make one side of the leg nerve nutrition is restricted will appear leg numbness. This is a more serious problem, you should go to the hospital in time to ultrasound examination of the lower limbs, once found to have thrombosis should be immediately hospitalized for treatment.