Mine just started to do the same thing today... But he is laying on his side and inching around the tank slowly, just moving his feet. It apears that he ripped his arms (smashers) off. I am hoping that he is going thru his molting and that he just having trouble getting out of his shell... Its pretty rough to watch this insane mantis shrimp that is fast as lightning to be reduced to this helpless organisim that just lies on its side...
I had just moved the tank yesterday, and not being the brightest forgot to plug the heater back in. But I doubt the temperature dropped below 65, and I assume they should be able to handle that. After all I would imagine the gulf is around that temp now if not cooler.
So I dont know if my mantis is just mid mult... or I some how hurt him in the move. only time will tell I guess