I think you simply burned out from that one year of constant work, but somehow are in denial of the burnout.

At least this is the simplest explanation - the first thing that comes to mind.

Also, you might be overanalyzing and just being a bit too cerebral for your own good - everybody knows that it is impossible to be constantly motivated, and they know it intuitively and intuitively have gotten it right, without ever having read a single word about neurons. So maybe relaxing a bit and going with the flow + implement the many helpful tips from this thread, and you would be OK. Reading satirical or humorous pieces would be helpful for you as well, or simply watching funny videos on youtube - whatever takes the cerebral edge off your internal process.