It's because you don't have muscle weakness but instead, you have muscle fatigue. This is undoubtedly because you haven't been eating quite as well, not sleeping well and your level of anxiety. You have "muscle loss" because you have lost weight . . . not because of true muscle atrophy due to any type nerve or muscle problem.
It doesn't sound like you need to be scared of anything; what you have shared does not sound life-threatening. I think part of the reason things have taken a turn for the worse is that you're not eating or sleeping very well (I know you're not). Your constant worry is making things even worse. Relax and recharge your battery. It will help immensely.