O/U should be tough and challenging causing you to mentally dig deep, but shouldn’t bury you. If you’re smashed barely holding on and have lost cadence and form then something is not right. Maybe you need a small reduction.
I was the same way when my FTP was too high…
With a 4% FTP decrease my workouts went from ripping out my soul to a tough challenge that takes mental fortitude, but still leaves me rested enough a couple days later (both physically and mentally) to hit the next hard workout. I no longer dread the workouts wondering if I can hang on again, but rather look forward to the challenge.