A brush with death? Does anybody know?

My yellow tang is dying i think. No apparent reasons(parameters are fine). He's at the bottom resting on a rock. I took a look with a mag glass, and no leasions, the convict tang and him had been frisky lately, showing OFF, but at one point he turned and i was able to see his other side. Clear , no scar, or leasion either, good color too. He look exhausted. Could it be fight exhaustion?? This morning he was fine and ate, good stamina. I Did some feeding dose my supplement as usual, the only thing i added was iron since it was at 0.0ppm and it was the ordinary dosage like usual.













Nope he's upside down now (3h later), my theory now is he might of been cornered by the clowns and hit the nem with his belly, see how high her mantel was this morning ....he was too active this morning to come down so fast , to be symptomatic , and environmental....all the other fish seem fine, The only thing i don't know is; does a brush with a nem's mantel leaves traces or scars on a fish, or if its even possible that a fish can escape that.