I understand there's a rare chance of recurrence with hepatic lipidosis. You should probably get him checked just to be sure.
You aren't crazy, trust your instincts. you know your cat better than anyone.
Poor little guy! Feels crappy, and it sounds like something in his lower back is bothering him?
What I love about vets (if they're any good) is that you can go in and say "He isn't quite right," or "She isn't herself," and they don't give you the look you get from a people doctor. My vet knows if I say, "She doesn't feel well" that she doesn't feel well, and the job is to find it! [In my next incarnation, I'm going to skip drs. and go directly to the vet.]
What I DON"T love so much about vets is that I wrote a check for $417 to the horse vet yesterday for two trips out! Dunno what made her think I even HAD $417.... If my poor baby has a problem again, she's gonna have to get her sick little rump into the trailer. This time, though, the vet gave her a shot of something, and she basically climbed into my lap (tougher with a horse than a cat, if anyone asks) and went moribund--might not have been that great to get into the trailer coming back.
Since your kitty has been sick, you might want to be a little skeptical of normal bloods. Those things vary depending on what he's eaten recently, etc. And you really, really want to catch it soon if it's coming back, I think.
I suppose the good news is that if he's having an organ function problem and had a normal screen, it's just starting. Your instinct is good, not to ignore it.