Nems are weird and do all sorts of odd things...if he stays like that for a long period of time or starts spilling messentrial filaments from his mouth then you need to worry...
Well what do I know??? After hours of panicking he perks right back up like nothing ever happened. Man I was just waiting for him to start jezzing all over my tank . Cool beans ‘Reef Lover
You don't have to feed a nem if you've got decent light, but you can. My own guideline is to feed not more than once a week, no food pieces larger than the anemone's mouth, and remove the food if the nem doesn't actively grab it immediately.