Nietsoj
I had the same problem playing in a World Open. The schedule was two games per day for four days. The way I approached it was to quit playing/studying for two weeks prior to the event (I had been working hard for several months) in order to build an appetite for chess. I didn't participate in post-mortums of my games, I didn't play blitz, I saved all my energy for the rounds. I went for walks (@1/2 hour) prior to rounds to relax me. I rested as much as possible between rounds, sometimes just lying in my bed but not sleeping. It worked pretty well--I went 6-2 but blew a win in the last round or it would have been 7-1. Hope this helps!
I have registered for my first ever OTB tournament. The tournament is a 4-day event with 8 rounds, and the schedule seems quite compact in my opinion. The two first rounds are rapid (30 min), and the remaining rounds are 90 + 30 min with 30 sec increment.
When thinking about this schedule, I suspect there is a very real risk of fatigue. Playing 2 long games the same day seems like a real challenge. Not to mention that this is repeated two days in a row.
What are your suggestions for how to conserve and maintain energy and avoid fatigue?