Damn that sucks, sorry to hear that
First off as a suggestion, I have this rule, its just something I've learned over the years. And that is never mess with the tank just before you're going anywhere. Just as I've learned, never mess with the skimmer just before you go to bed. No good can ever come of it (fricken skimmer, it took me a few times and many towels to figure that one out
).
There are many possibilities, you said you moved stuff around? Possibly disturbing a nasty pocket of H2S in the sandbed? Did the powerhead you moved slip and blow into the sandbed? Perhaps the algae scraping stressed them out?
How long has the tank been set up? How big is it?