For most of us, before we begin meditation practice, the only time in our lives when we are totally still is when we are going to sleep. So sometimes when we sit down to meditate our bodies think “Stillness? Must be time to sleep.” So sleepiness is to be expected when beginning with meditation.
The first thing to try in combatting sleepiness is straightening the posture. Typically, the first think that happens when we start to get sleepy is that the posture wilts. Conversely, actively lengthening the spine helps to maintain alertness.
The second thing to try is opening the eyes. The light will help to wake up the brain. The third approach in the escalating response to sleepiness is to stand up and continue the meditation practice in the standing position.
If you are still falling asleep while standing with your eyes open, it is probably time for a nap!