Too many of those and you just want a dark room to huddle in!
Pretty much what happens.
12 hour days during the summer, 900 hours plus per year for the instructors. Days off you are taking planes to maint solo otherwise you you don't have anything to work with on the days you are working.
And its still happening to this day. Last time I did a full day instructing I was absolutely shattered. And gawd knows how I managed doing 6 days a week for 4 months straight during the summer.