pascha, I’m not a posek so don’t go by what I’m saying but I think that if you don’t feel well and the only way for you to make it through the fast is by staying home and even staying in bed then that’s what you gotta do. I have family members that don’t go to shul (even for yizkur) because they would not be able to make it through the fast otherwise.
I also know for myself that ever since I was released from the hospital (a year ago, b”H) it’s hard for me to sit for crazy amounts of time, like sitting/standing for the entire mussaf so I do plan on leaving in middle if I feel the need to and I don’t feel guilty for doing it either. (wow, that was a run on sentence. Sorry) I try to make it back for neila but again, if I see I won’t be able to manage it then I try and say it at home by myself.
Good luck fasting and gmar chasima tova!