Oh man, I'm so sorry that anxiety is sitting with you right now - it stinks. I too have heard that mood swings can be part of the early stage post-surgery for a variety of reasons, including hormonal fluctuation, sleep disturbance, or loss of food as a comfort and coping tool. During my pre-surgery phase, I got more aware of how I have used food to manage and numb anxiety. Post-surgery, as my hunger/food desire has started to return I've had some unpleasant reminders of this old habit.
I also really and truly get having fear around moving from one food stage to the next. with each food stage "graduation" I have been so afraid of what might happen. Go figure that by following my program I have been fine. Like catwomen said complications are rare, and even rarer if you're following the recommendations of a reputable program.
Not to go into advice mode too much, and knowing our experiences might be different (maybe you are having panic attacks rather than generalized anxiety?), I will say that I have found therapy to be a big help. With my therapist I know I can unload my anxious build-up. saying my fears out loud to someone else helps me put them in perspective. Therapy also gives me a non-food outlet that instead of numbing helps me identify what might be contributing to anxiousness and give it less power by helping me to put it in perspective. Not all therapists are skilled, so it can take some shopping around, but might be worth it.