You're not going to be up for helping out other people today. It's not a selfishness thing; it's just that you are too busy and won't have enough time. There are real limitations on your resources right now, so don't take on anything new: you will definitely regret it, probably before the end of the day. Stick to your guns and avoid associating with people who always seem to need your help. Let them figure out their own answers on their own time.