All loaches possess very sharp, bony spines behind their eyes that they can unfold and use to warn off other fish (and the occasional fish keeper who insists on taking them to shows).
I came back about 15 minutes later and he was dead with a boney spike about 1/3" long sticking out of the left side of his head, right near the eye. I have no idea what that is, or where it came from. There is nothing in the tank he could have jabbed himself on, and it looks like whatever it was went out rather than going into his skin...I'm guessing that's what the problem is, but what is it???
Clown loaches have spines on the sides of their heads. They extend them when in distress so it's not a surprise that in its last horrified moments of its life it would do that.