Your symptoms are concerning. There are many possible causes of your conditions -- some of which are minor and some of which are very serious. I would strongly recommend that you see a neurologist
( a brain and nerve specialist) to have this evaluated.
The sensation of limbs falling asleep is medically known as a parasthesia. This is often caused by irritation to the nerves. This "irritation" can occur anywhere from the brain to the nerves in the skin. One common concern for irritation of the brain is Multiple Sclerosis or MS. MS is a condition where inflammation of the brain causes weakness, numbness
, visual changes etc that often come and go. It is possible to have a normal MRI
at one point in the course -- as the inflammation comes and goes. I would discuss this with a neurologist.
It could also be the nerves outside of the brain causing the problem. Known as a peripheral neuropathy, this can be caused by low vitamin levels (like b12), thyroid problems, infections (like Lyme's or syphilis or HIV), or other cancers like multiple myeloma. There are certain tests of the blood that can help.
Talk to a neurologist. He or she can help diagnose and potentially treat your symptoms.