Hi, Several things do come to mind, one would be that you may have a small area of arterial vascular stenosis meaning that the blood vessels providing fresh blood to the leg is tight and constricted.This reduces blood flow to the leg and can not only cause the leg to fall asleep quickly but also case it not to regain feeling for some time (minutes in some people). These types of stenosis can occur due to trauma or prior bone fractures or even some people are born with them. Another potential cause along the same line is arterial occlusion due to cholesterol build up in the arteries. It is the same idea but here the cholesterol has built up to a degree that it is now reducing blood flow in the same manner. Also, certainly metabolic conditions can also cause this, auto-immune vasculitis, or even hypothyroidism could potentially be the cause. What I would do is speak with your family doctor about first obtaining an arterial ultrasound of the legs, this will determine if there is a stenosis occurring and from there further testing if needed can be obtained but it will tell us if there is any focal point in the artery causing reduced blood flow. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. David Girardi, Internal Medicine Specialist