Great post. Very useful for people are in that hole, or people surrounded by lethargic friends or loved ones. I have not personally been in that state. I try to always do something, either intellectual or physical work. Can't remember the last time i spend a whole day just doing nothing, resting. But, like anyone, at some point we downs and it is easy to succumb to lethargy, especially in bad economies where frustration can get get the best of you.
It's complicated, but you say, it can be overcome with both external and internal help, unless the thing becomes drug-dependent.