I am experiencing a dull numbness/tingling in my left leg which has moved to my left arm. Most noticeable when I lie in bed or sit down. What could this be?

Neurologist. Numbness,tingling in left arm and leg occurring simultaneously may be seen in right carotid artery blockage, right cerebral cortex pathology but may also occur in demyelinating disorder like multiple sclerosis. In ms the symptoms may occur in a scattered pattern,however. A neurologist is best qualified to evaluate and advise you.