My first thought would be a shower chair with a handheld shower head on a hose. Then it's not so physically demanding and if you do panic you can sit and deal with it. You can get them at drugstores, Walmart, Amazon........It might also alleviate pain and fatigue that you are dreading and thus decrease panic.

I used to be very paranoid about showers and so I did sponge baths as often as possible. I kept things as open as I could so I didn't feel trapped: clear shower curtain, door open so I could see and I made sure the house doors were locked before I tried it.

I'm not sure what else to suggest. I'll think about it.