I'll preface this by saying that I don't want to invalidate or diminish your experience, this is genuine curiosity. If you can't get up, have weak muscles and no motivation, how do you do morning exercise and stick to a plan? I feel like pressure that something has to be done could be called a form of motivation, but again I'm not sure.
As I said, for me depression also manifested as a set of very negative sensations (you’re almost dead, feel like sort of hangover). After doc said that I can fight it, I became very angry at it and wanted to punch it in its face even with my numb hands, and that was a big part of that morning momentum buildup. It wasn’t a positive motivation, like “If I do some aerobics I will feel better”, it was more along the lines of “I hate your rule and you will die with me”. Thinking of it more, you’re right, it is motivation, but with a non-trivial connection to the result.
He probably knew me well enough to suggest the right plan, or it was just a good guess. Because anger and revolt are my base personal traits, and depression couldn’t take it from me that easy. E.g. being sometimes anxious, I often make self-exposition just to spite these feelings, instead of fleeing from their source. (Please don’t think I’m non-civilized though, it is completely internal thing.)
As of formal diagnosis, yes that was completely it, in an acute form (i.e. not chronic).
Edit: also I listened to Jocko Willink speeches in that state and understood them sooo well. He was so obvious. Now when my usual reasoning returned, they sound a little funny. It’s like two completely parallel worlds.
If the mind over body thing doesn’t work, try very very gradually increasing intensity without regards to time. When I’m feeling really awful, I’ll slow jog/walk less than a mile on the treadmill first thing in the morning, then come back later to do a proper run. It’s like taking all day to warm up, and it usually works if I can muster the will.
