In my experience, snails in general fake death a lot. o.O My mystery snail was the worst but nerites can be real brats about it too. What I hate is when the mystery snails start floating for no apparent reason.
I'm glad that Matt is there for you, though. It would be rotten if you had to go this alone.
EDIT: Raz, in fishkeeping, learning never ends. :) But Raz would have had a very sad end on a lonely shelf if you hadn't picked him up and given him those months of care and love. He passed in the comfort of love and with the dignity every fish deserves, not laying there decaying in a dirty cup for a week before someone noticed.