Re: numbness in both arms
Make them do an MRI. Yes the disc can be the problem. Did dr say why they thought it wasn't? Do you have other symptoms, pain, weakness at other times, or any other thing going on in your arms?
C6-7 could be pressing on nerve roots or cord, can cause numbness down your arm, at your deltoid, all the way to your hand.
You sleep on your back, my problems before surgery used to get irritated by sleeping positions, kinked neck etc. that can happen even on back. A very easy way to see if neck positions aggravate it is to sleep in a soft collar and see if it improves.
If this is a continual problem, like not just one or two random occurrences, then get to a neruo or a ortho spine guy! Take care.