Make sure to get a full night of rest before! Also, when they give you a break during the test. TAKE THE BREAK!!!! Walk outside, do NOT think about the test and don't forget to breathe (your brain needs all the oxygen it can get!!)
Also, during the real test, I actually don't remember getting tired at all because I had adrenaline pumping through me the entire 3/4 hours of it.
If you're still worried, I would just do more practice tests to increase your endurance 👍