It might be water quality issues so do a big water change ASAP, check the temperature as well as your heater may have broken. Also what sort of pleco is it and how old is it?
No i don't think eating a snail would do that. What other fish have you got in the tank? How big is your tank? Are any of the other fish acting strangely?
no every one else is fin i have a 10 gallon kinda heavily stocked but just till i get my 40 fixed....
2x cory
1xbumbleebee goby
1x 2in rainbow shark
1x2in horse face loach
1x angel and my poor pleco
and a some pea size snails