Accidental Death..

This sucks...
I got home tonight late, and my light had already timed off(set to go off about 10 pm). I turned on the room light, and a few minutes later started my normal nightly visual inspection of the tank. I noticed one of the mud minnows "flipping" around, obviously not long for this earth..so instead of trying to catch it, I allowed it to expire(only a few more minutes).
The fish appeared in perfect health except for the fact that both eyes were bulged out, and filled with blood. It was in otherwise perfect condition, had apparently even eaten tonight(I have a healthy colony of blackworms established in the tank, so the mud minnows and darters generally feed at their leisure).
The fish were all perfectly healthy when I went to work at noon.
I can only assume that the fish panicked when I turned on the room light, and ran headlong into the side of the tank or a rock or something...
Other then one dying a day or two after I put them in...this is the first mud minnow I've lost, now down to 4(gave one away earlier), and it was a stupid accident!