Never underestimate the value of sleep.
During meditation retreats we like to say that sleep is king. By that I mean that it is good to get to sleep early so that you are fully rested for your daily meditations. If necessary, take a nap in the afternoon, so that you are fresh for your evening meditations.
Remarkably, upon hearing “sleep is king,” some choose to sleep through their meditations. Oh my, how easily the knowledge is lost. If sleep comes during meditation do not resist it, but structure your life to make the most of your meditations.