It's likely burnout. I have experienced this for a solid year now. Just sit at my desk for 8 hours a day unable to get any real work done. Have probably 30 minutes of real productivity a day. Started after working insane hours for months and months on end. I refuse to work more than 40 now. Funny thing is I get great reviews because I just decided to hijack a team lead role that was missing and just run the team. No one knows how absolutely fried I am. My opinion is that humans are not meant to just sit in front of a desk producing useless widgets that do no real societal good besides making money for our employers. We have no sense of purpose. We just make dumb shiny things. I am still struggling with it. Starting a new job soon in an official management position, optimally I am happier there.