When you feel that way, do you find you need to drop everything and attend to it? I picture myself more like, "That's interesting, I feel down and yucky right now. Wonder what that's about?" -- and then I'd either go on with whatever was in front of me to do or, if worst came to worst and I found I wasn't up to it, take a nap. For me that seems to be the miracle cure.

I do make some allowances if I'm feeling "off" -- I might be extra careful using power tools, for instance, and keep a close eye on whether I was having any near misses.

I'm sorry to hear about your friend. I know that's a scary diagnosis and I hope he/she gets good treatment and does well. Keep noticing what you're feeling about your friend, even though it may be hard for you at times -- letting it come up almost always works better than stuffing it and having it run you. Was the "down and yucky" that you mentioned in response to finding out about your friend, or before?
That's what it's like for me when I've got a lot of stuff going on that I haven't managed to sort out yet. Try giving yourself some time and elbow room to work on it. Just that much often turns out to be enough.