try to find a game that isn't so close to your bedtime, if you are still in the game - then take a break - sit out for a few minutes and go outside for a bit etc.
are you a 1 table player ....
try like 6 at a time you will be so busy trying to keep up with things sweat will start beading up .. and your will probably play better too because you wont have time to mess around with junk cards that might make a single table player want to speculate raise your edge
Maybe it’s because ur waking up early in the mornings or that ur not getting enough sleep. Maybe try taking a nap before u plan on entering a long tournament or start drinking coffe.