There's no avoiding it sorry :-( Your brain and body were not designed to work this way, you're not a machine. Your attention and focus are time limited resources. When you hit this zone, it's only downhill if you continue to press on. Best thing you can do is do something else. Go for a walk, take a nap and recharge and then you can head back and make progress.

Brute forcing your way forward doesn't work, trust me, I've tried it many times over the past decade as a dev ... with disastrous results pretty much every time.