is it depression or worrying?

I don't think I've really ever posted here when it comes to "me."  But, I think it's now time that I do.  See, I don't know if I'm going into a depression or if it's really just stress and worrying about my friend.  I found out recently that doctor orders have now prevented her from going back to work for a while.  She said it would be like this past summer just cold.  I don't want to become depressed because when I do, I can do some really bezerk things that are, in a way, out of the norm.  It's nothing major serious but until I get older and out from under my parents' (mom's) wing, I'm pretty much stuck between a rock and a hard place.  Got any advice?