HELP! CAT ISSUES!

So I got out of bed to call my supervisor and tell her I won't be coming in to work today because of back problems, and I hang up the phone and to my horror, Ekho is dragging his butt across the hallway floor and pooping the whole way! HELP! What does this mean?! Is he sick? Will he keep doing it? I closed him in the bathroom with his litter while I cleaned it up, changed his litter (it wasn't FULL but it was nowhere near empty and it sounded like he was flicking it around before the butt dragging incident). I kept him closed in the bathroom while I did a quick google search, and I can't seem to find anything, but maybe "dragging butt and pooping" isn't the correct search term. He kept meowing to get out, so I took him in the tub and washed his butt (he still had nasties there) and then let him out. He's now grooming himself by my chair.... anybody have any great insight into cat behavior? Is there something I should do, or was it just that the litter was too full for his liking, so he decided to poop on the carpet? HELP! I've never had a cat before.

M