The first 2 months of lockdown, I was crazy productive, working till midnight every night. Then little by little I'm slowly finding it harder and harder to concentrate. My productivity has fallen enough that my manager has called it out. So, at this point the commute and my eating habits have been the only thing that has significantly improved from this WFH lifestyle.
Go take one-two weeks off if you can, seriously. Even if just to stay in your area, maybe do some park/nature walks. The reset truly helps. The need for vacation didn't go away because of quarantine.
If you've watched Red Dwarf, the entire reason that Rimmer was brought back as a hologram, was so that Dave would not go insane.
And another crew member could have been brought back, but Holly determined that Rimmer would be best. The conflict, you see, was required.
Many here decry the "waste of time" of being interrupted. Their attention divided. Yet you're indicating that after a few months of endless, day long shifts free of interruption, productivity has dropped a bit.
It appears for some, Holly was right. You need a Rimmer.
Productivity has nothing to do with how long you work... but working until midnight does sound like a recipe for burnout. You should take a break to reset, as soon as you can!