The possible reasons for non-stop leg flexion and extension after falling asleep may include fatigue, calcium deficiency or mental stress. 1. Exhaustion: daytime strenuous exercise or prolonged activities, resulting in leg muscle micro-injury, when falling asleep to maintain a posture for a long time may lead to slow blood circulation, fluid reflux in the tissues is impeded, stimulating local discomfort and the phenomenon of non-stop bending and stretching the legs. 2. Calcium deficiency: generally older people, less calcium absorption, discharge more calcium deficiency, calcium deficiency is prone to dreamy, irritable, may also appear the phenomenon. 3. Mental stress: because of the special things that lead to mental stress, it is not easy to fall asleep, and even if you fall asleep, you may dream a lot, and sometimes it is manifested in the phenomenon of constantly bending and stretching the legs after falling asleep. There may be other reasons why you keep bending and stretching your legs after falling asleep, so you should go to a regular hospital and get proper treatment from a doctor according to your condition.