Like I said............Fish get sketchy sometimes and check out on you for no reason. I think in the first 6 months fish can check out and you won't have any clue what did it.
stress kills. how would you like to be netted, put into an air tight box, drug across the ocean floor and then let out of the box once you got to the other side of the ocean then be in a place where you didn't know anyone and had to change a lot of things about the way you lived.......
I know it's not the EXACTLY the same thing, but still.........it kinda is
My vote goes for the fish was healthy and had an anxiety problem, sketched out, and died.
Don;'t rack your brain trying to figure it out, fish that are two months old have a very high chance of checking out on you for no reason..... that's why you shouldn't name your fish until about 6 months in.
Think about it like this....... I've got a clown(a gold stripped maroon) that is about 8 years old I think. I got it from my LFS
when a guy brought it back because it killed something in his tank..... it also nipped his finger. Anyways I took it home and had him about 6 months. then one day he was missing the entire top of his head, the skin was missing all the way to the skull and it was all torn up. there was no other fish in the tank with him and the water tested fine. I don't think it was a parasite or anything either because he had been fine or 6 months prior. I do not know what was wrong with the fish. anyways his head was jacked up like that for about a week and he was basically just laying on his side on the bottom of the tank... then one day he was fine. I didn't do anything except leave him alone..........
what does all that mean....... beats me. It does prove my point that some fish are just naturally sickly and have a shorter life span than others................ humans do the same thing you are saying happened to your fish, it's called SIDS.
so again, Sorry to hear about your loss, but don't rack your brain to hard trying to figure it out...... the reality of life in the big tank is that things die.