It’s most likely just pushing out the bolus of rotting food to make room for more, the mouth on a nem serves to both take in food and expel waste...by tomorrow it should look much better and be back to normal shortly after that!
If there is residual heavy metal contamination from the use of tap water killing snails and inverts then it might be doing the nem in as well....i would do as suggested in other thread run more carbon and get some poly filter of some sorts to remove it. Best of luck....
I just Bought this purple Haitian Anemone and it’s shriveled up like this. My water parameters are perfect for this little guy. Can you tell me what’s happening?Is this normal right after you put it in