I only feed my fish twice a week. Sometimes once a week depending on what's happening in my tank. I don't know if your fish will pull through but you don't need to think it's starving to death just because it's not eating immediately. A water change can be quite a shock and it may just be too stressed to think about eating right now. Don't blame yourself. You're doing everything you can.
@gladrial
I’m mostly worried because he’s a bad eater to begin with, and I just got off of vacation, where he had a pet sitter for 8 days, and I have no idea how much food he ate in that week. The pet sitter overfed him grossly, and the tank was in really bad shape when I got home. He hasn’t been his active self since then, and the 100% water change I had to do only made matters worse. So I really don’t know how long it’s been since he’s eaten- his body condition doesn’t look good at all. I guess the only thing I can do is wait. It’s the last time I’ll get a petsitter without looking into them extensively.