Well, a common symptom of Depression and Anxiety is numbness and dullness of emotion. But the usual culprit of this lack of enjoyment is Depression, a lot of people(including me) who go through Depression often feel this way. Depression also heavily disrupts people's focus and they can't process work a lot of the time(also like me.) People with Depression also can't open up to people well, are usually exhausted/tired and sleep a lot(or have unstable sleeping patterns.) When it comes to Depression, it's not always about feeling sad. Sometimes it can just be about feeling incredibly empty. I know you said that this likely isn't Depression for you, but I'd beg to differ. All of the symptoms really do correlate with that.

I may be wrong, though. I just really think that's the case.