Your muscles are not devoid of blood flow or you would have a serious problem that would need medical attention.
You might want to ask your doctor about this feeling you have, but it could be just in your imagination so try to relax for a while and see if it goes away.
Did you recently start the medication? This could be a side effect if so. If you truly feel your legs are functioning less well, you're not moving as well, and you've become impotent, have you considered seeing your doctor?