How alert you feel is determined by structures in the center of your brain.
These structures get input from the front and back sections of your brain (the cortex and the cerebellum, respectively).
The front section of your brain provides what’s called “top-down” input. When you use self talk to tell yourself to concentrate, you are providing top down input.
The back section provides what’s called “bottom-up” input. It carries messages to your brain from your muscles and joints. Its called proprioceptive input.
If you have been exhausting yourself using the “top down” type of input to regulate your alertness, then you can try some of the bottom-up type.
The idea is that you engage your muscles and joints, whenever you want to speed up your engine (feel more alert) or slow down your engine (feel calmer).
You’ll need to experiment with what works best for you.
See entire post from Dr. Alice Boyes: Regulating Your Alertness (for Study, Work, etc).