I hear what you're saying. Much like you, I've always been able to make myself function even during very severe depression. This episode I'm in now, I make it to work but spend my evenings and weekends in bed or on the couch. I've been trying to "will" myself into functioning for 2 months.

Anyways, I'm certain that the way depression feels changes episode to episode. Different make up of symptoms each time. Lethargy must be prominent in your current episode. Be gentle with yourself. It is not your fault. All you can do is keep trying.