What happened?!

[OCDP]

I bought a purple firefish yesterday from the LFS, and some frags, came home.. put the fish in, and it did it's normal firefish thing (went and hid) .. which was fine.. it did that for the entire night .. looking fine. I wake up this morning and it's dead... mouth wide open, body all still intact... but dead... I am so mad, and I have no idea what caused this.

If anyoen could help me out in figuring out what may have done it for him that would be great... I'll start off by saying paramaters are fine.. all other fish are fine... etc... it was housed with 2 true percs (who dont leave their anemone for nothing) and one yellow watchman goby.

I am so mad ...

Scott