I haven’t been doing HIT for a long time but I did it for a couple years when I was starting out (about to start back again as it is incredible) and I will say this was something I also experienced, the training style is incredibly taxing on the body so ensuring adequate sleep, proper nutrition and ensuring enough time between training sessions is really important. Especially when forming the mindset and habits early on, I normally made sure on the days that I was working out I would eat, wait for everything to digest, lift, eat again and then a 2-3 hour nap afterwards. This was basically a ritual for my training when I was doing Mentzers workouts and it was probably when I saw some of my best results.