It really depends, I try to listen to my body and think of whether I’ve had enough water and food and sleep, then fixing the issue accordingly by either hydrating, eating, or taking a short nap (or doing yoga nidra).

If none of those are the issue or if the nap is not possible, I will try some caffeine (coffee in the morning, cacao in the afternoon).

And if I have a chance, I will listen to some brainwave music that stimulates beta waves in the brain for concentration.

Finally, meditation helps me. It can be a nice pick-me-up and an opportunity to recalibrate and reset.