September 14–20 is Invisible Illness Awareness Week. If you have friends or family members with health problems, now would be a great time to give a call, see how they're doing.
What's that you say? You haven't spoken to them in a while because they never stayed in touch? All the more reason to call. Chances are they really do want to maintain contact with you. They've just been too overwhelmed by their illness and activities of daily living to manage it.
If you don't know what an invisible illness is, look over here.