While it sounds like this has turned into an irrational level of anxiety, sometimes approaching fixing things with rationality can still help. I have struggled with similar anxieties surrounding my physical health and I think that the thing that would help me most in this situation is prioritizing controlling the reflux in any way possible. Ie, tons of research, talking to doctors, trying all different approaches, etc. However, it does sound like you could also benefit from general maintenance tactics to keep anxiety lower like therapy, medication, and regularly practicing mindfulness techniques.

Could you bring your desk chair over by your bed for a few nights in order to start getting used to the bed again? Maybe resting your head on the bed but keeping your body on the chair? I also agree with the others that a therapist would really help. They would have the resources and plans to truly help.

I think that's an understandable concern!! Especially when it comes to something that can make you sick so easily. If you are able to, working with a therapist on the mental/emotional aspect of it, while (if you haven't already) consulting your doctor for other things to try to help in the physical aspect. Prilosec worked wonders for my mom so maybe see what your doctor has to say about it? When you sleep at your desk do you lean forward on your desk or lean back into your chair? If you tend to lean back, there are angled pillows you can get that allow you to be in a bit more of a leaned back position instead of completely flat? And the same could be done for leaning forwards with a thick yoga bolster (I know I've fallen asleep many times on mine 🥴).

My first thought is hypnotherapy. It can work wonders. Especially since it's just an association you need to reverse. Worth a shot..?