My XAH is still, as far as I know, "functional", in that he's not raving drunk every day. However, having lived with him, I remember just how difficult it was for him to simply get through the day. It's like he simply did not have the capacity to deal with the usual stresses of life, and instead medicated himself with alcohol, sleeping pills, codeine, video games, and junk food.
In a sense, "functional" was just this facade he showed the outside world. In reality, he was being held up by a number of things, including me.