- at least in my tank - seem to always go through a "funky" stage every once in a while. I've never been able to put my finger on the cause, but they always seem to come out of it with a growth spurt. My guess is that they are conserving their energy - the energy they'd normally use to expand their tissue is being used to lay down new skeleton, or ready themselves for more growth.
can suck down pretty tight to their skeletons and look pretty scary, but still be healthy. Hopefully, that's all it is in your case. As long as you can't see anything obvious causing the problem, all you can do is keep the water in good shape and let it be. If it's feeding at night, that's a good sign. Agree with Mitch... a little mysis when its tentacles are out never hurt!