Ok, so I really don't want to have to go through the battle with Grimgnaw again, because that sucked. But coming out of it I have a pretty major decrease in str, and I can't get rid of it. I've rested and tried restoration stuff, but nothing works. I didn't see for sure how I got it...that fight is pretty darned hectic as it is. Any help appreciated.

It's probably due to sneak attacks, or possibly the result of one of the spells. Greater Restoration should be able to fix it right up. I don't think that anything less than that will do it.