Woke up this morning & my left leg (from knee down) was numb. I was sleeping on my back, my leg was to the side & bent. Can the position cause numbness?

Yes. You may have pinched a nerve in the position that you were laying in. This is very common, and usually resolves itself after a few minutes of repositioning yourself.
Possibly. If the numbness was due to the position you slept in, then the numbness should resolve. If it does not, then see your doctor.

Related Questions

Toes are numb off and on not asleep but as though in ice. Left leg behind knee on right side-artery? Extreme Pain getting up, hrt issues est. Concern?

Yes. If you have a history of blood clots or concerned about clots due to hormones, you need to see a doctor ASAP. "Extreme pain" in your leg could be a DVT (clot). Discuss intermittent claudication vs nerve compression with your doctor regarding the paresthesia o the toes. Read more...

Pain in my left leg from my knee down a lil numbness in my toes, I do have lower back problems can that be the cause? Also weakness in the am both legs sometimes

See a back surgeon. You may well have spinal disc disease with consequent pressure on nerve roots exiting the spinal cord. Get this taken care of before you have permanent problems. Read more...
Probably nerve . Quite often a low back problem may be causing a nerve irritation. You will probably need to have an orthopedic exam, x-rays and ct scan and emg. The treatment may be office based or require more intense therapy. Read more...
Numbness in toes. If you have pain in one leg and have lower back problems this could be a symptom of lumbar radiculopathy. This condition causes referred pain or numbness down the leg and into the foot. Rest pain (its worse when your sitting or lying down) is more indicative of nerve origin. Pain with motion is more typical with a musculoskeletal origin. A neurologist would be best to determine the origin. Read more...