I usually don't get sleepy while I'm playing, unless it's late at night, which I try to avoid. However, there are times when I feel that the game is too slow. In those cases, I usually play a podcast or something interesting in the background. I avoid things that require too much attention so I can stay focused on the game and pay attention to my opponents.
If the issue persists outside of poker and becomes a routine problem, you may need to pay attention to your diet, get more sleep, or consult a doctor if it becomes a daily inconvenience.
Something that helps me when my mind wanders too much and it's one of those days where staying focused becomes a challenging task is exercising and taking cold showers. (The truth is, I do it anyway, whether it's a good day or not 😅)