but is it muscle atrophy or is it just glycogen and water dropping off from being in a slightly de-trained state? You might be surprised how much a muscle can fluctuate in size based on water/glycogen. If you haven't ever done this, try to go on a mild diuretic (like dandelion) and drop carbs out of your diet...you'll probably lose a lot of size over a week but it won't be muscle atrophy
I'm not the biggest dude in the world but I hold a good amount of muscle around 10% bodyfat or less at certain training phases. I compete in actual sports and am not just a gym rat/bodybuilder.
Mental issues are RAMPANT in the bodybuilding community. Body dysmorphic disorder for starters. If you think muscle is truly atrophying after only a couple weeks away from the gym, you need to talk to a therapist/counselor. That's all I will say. I'm not qualified professionally to be able to help at all for that kind of issue.