Back in my uni days, and then in my early career, everything was done to timetable, 24/7. It got a bit ridiculous at work since there was so much to do, more than I could ever accomplish, but I pushed myself to get as much done as possible. At that stage there was no respite at all.
After eight years of this kind of pressure I started to fragment and I developed bipolar. I can't say how much the pressure had to do with the development of mental illness, if at all, but it is a good start to trying to understand the processes involved. I remember that at one point my brain just froze and wouldn't do any more.
I'm trying to rehabilitate myself into at least doing a couple of chores before bed. Other than that my brain refuses to be scheduled. I am frequently late, or forget appointments entirely. I do not diarise anything before midday. Sometimes things are 'just too hard'. Back in the old day I never would have allowed that.