Health struggles are making it tough to keep up with salah

As-salamu alaykum everyone. I've been having a really rough time health-wise. I got a bad stomach infection that needed strong antibiotics, and between the after-effects and my current meds, I'm just constantly tired and lacking energy. I hardly even go for a walk anymore. To make things harder, the summer prayer times where I live are intense – Isha is so late and Fajr is only a few hours later, right in the middle of when I desperately need to sleep. I know praying on time is best, but proper rest is essential for my recovery. I'm also slowly coming off an antidepressant, and if I don't get enough sleep, my whole nervous system feels off during the day, which then makes my stomach issues worse. It's a miserable cycle, subhanAllah. So I have to ask... given all this, is it permissible for me to pray Isha and Fajr *after* I've gotten my necessary sleep? And can I pray sitting down? The physical act of standing, bowing, and prostrating feels like a huge workout right now, and even going slowly makes me more sleepy. I know this might sound silly, but I feel stuck between not praying properly and not praying at all, which is what's happening now. Any compassionate advice would mean so much, jazakAllah khair.