Numbness in joints and limbs can be the result of several aspects of rheumatoid arthritis.
The first is that the inflammation from the disorder can spread to the blood vessels. This is called vasculitis. It results in weakened blood vessels that can rupture. Less alarmingly, the inflammation can slow blood flow, so the muscles in your limbs receive less oxygen.
Numbness can also be caused by the swelling of joints pressing up against your nerves. Left unchecked, this form of nerve compression can cause more pain and reduced limb function. If you leave the nerve pinched for long enough then the nerve can be permanently damaged.
So, while numbness from RA may feel similar to your leg falling asleep, it can have long term implications.