It's good to heed your need to feel socially useful, but do not let your altruism overshadow your personal responsibilities today. You can't worry about other people's problems when you have your own to figure out. A friend might try to play on your sense of guilt in order to get your help today, but you can't give it if you don't have the time. Putting their needs first will only make you regret your actions later on. Tell them you're sorry, but you can't step up today.