It is quite common to experience drowsiness during meditation. You become very calm and relaxed. That is exactly what is supposed to happen. When you find this happening, apply your mindfulness to the state of drowsiness itself.
Drowsiness has certain definite characteristics. It does certain things to your thought process. It has certain body feelings associated with it. Locate those. This inquisitive awareness is the direct opposite of drowsiness, and will evaporate it. If it does not, then you should suspect a physical cause of your sleepiness. Search that out and handle it. If you have just eaten a large meal, that could be the cause. So, don’t overeat; it’s not good. If you overstuff your stomach, it will make you even hungrier. I heard that someone in our meditation center eats a lot of lunch, and that’s the only meal he has per day. If you eat like that, your stomach will expand, and you will feel even hungrier, and easily get hungry in the evening. Moreover, it will be hard for you to reduce your appetite. So, don’t eat like that. In ancient times, people could have one meal a day, but they ate very little. They didn’t eat a large bowl like you do; they ate just a small portion. This is “one meal a day.” If you can manage to do that, it’s good. You can’t have a big meal all at once; that’s not good. And don’t overlook the obvious either. If you have been out loading bricks all day, you are naturally going to be tired. If I ask you to meditate, you might lie down after ten minutes. Do not give in to sleepiness. Stay awake and mindful, for sleep and meditative concentration are two diametrically opposite experiences. If you are very sleepy, then take a deep breath and hold it as long as you can. Then breathe out slowly. After that, take another deep breath. I have also tried this. It’s all based on my own experience. For instance, if you feel drowsy in the morning, you can take deep breaths. Keep inhaling, continuously and deeply. You can inhale for at least a minute, I guess. As long as you don’t exhale, then keep inhaling. The longer you can hold your breath, the better. Then, exhale slowly. After that, take a few more deep breaths, around three to five times, and your drowsiness will disappear. This method is very effective. When you feel drowsy, you can practice deep breathing like this—inhale continuously and deeply, and hold the breath for nearly a minute. Personally, I feel I can hold breath for around one minute to one and a half minutes, but it varies from person to person. Some of you might have shorter breaths; you are “heroes with short breaths.” It’s okay. Gradually, your breaths will be longer.