Indeed. I have never driven more than 4-5 hours at a time. I find driving very taxing for me. I tend to be very focused on the road and drive like everyone and everything is trying to kill me. For this reason I don't use driving aids either not even standard cruise control.

I find they help physically. After a few hours of driving I feel less tired and need to rest arms/legs physically.

The mental toll is nearly unchanged.

So when you stop I feel it’s easier to walk around and shop or whatever since I haven’t been applying as much force constantly.

But you still need that mental brake.

I find adaptive cruise control definitely helps with the mental fatigue as well, because I can concentrate on looking for hazards far ahead instead of having to pay attention to keeping distance to the car ahead. But yeah, I never drive more than a few hours without taking a break anyway.

Especially if they don’t slow down/swerve until the last second. If they had done it earlier you would’ve had more time to start noticing something was going on.