I've got to second Retro's answer.
It used to be
tiredness or sleepiness. And I don't mind saying that it can be a real bitch to overcome. I mean, you do the whole bit that is recommended in the discourses, splash water on the face, jump up and down, and the whole nine yards, and you're still just tired or sleepy.
So, how did I overcome this for good?
I kept reading the suttas, looking for another answer other than what was being obviously presented. Most of you probably aren't going to like this, because it almost sounds so obvious that we almost always overlook it. At first glance, you might say, "Well, sure. If I could do that, I probably wouldn't need to meditate. I'd have it made." And it does work! At least it worked for me. And I've never looked back since.
I've mentioned this before, but it's probably worth mentioning again. I was reading the MahaSatipatthana Sutta
(DN 22) and came across these lines: "Here a monk, having gone into the forest, or to the root of a tree or to an empty place, sits down cross-legged, holding his body erect, having established mindfulness before him. Mindfully he breaths in, mindfully he breaths out."
We've all read this before, haven't we? So, what's so mind-blowing about this passage. I mean, it seems pretty straightforward and boring, doesn't it? What could possibly be here that could revolutionize our practice that we haven't already done?
Well, I'll tell you.
It was the last five words of the first sentence that finally
caught my eye. I got to thinking. "You know, I really don't do this, do I. I mean, I usually get up in the morning, go through a quick morning routine, and then, because I don't have any extra time to waste, I sit down and begin trying to meditate so I can get on with the rest of my day. Very rarely do I take the time to establish mindfulness before I meditate."
So, I began to make sure I was awake in the morning before I began my sit (as often before, I would just start attempting to meditate whether I was fully awake or not, whether I was being mindful or not). Well, when I began to establish mindfulness before
meditating, that changed the whole ballgame for me. Suddenly, each meditation really meant something, and I was experiencing better and better meditation sessions. The mind was calming down more quickly, becoming still, and I was more alert and awake and able to contemplate better. My alertness increased big time, and my meditations became deeper and more profound with insight.
Many times, in order to make sure I was fully awake, I would take extra time to just sit and read for a while before meditating. Usually something that I knew would stimulate and enhance the meditation. Something that I could keep in mind as a kind of guidepost to what I wanted to be able to accomplish and use during contemplation. More times than not, it helped to set the tone for the whole meditation session by infusing the mind with a pathway to follow once the meditation began.
Suffice to say, I have never had any problems with sloth and torpor since then.
Here's another little trick you can use. At night, before nodding off to sleep, give yourself a brief post-slumber suggestion. It doesn't need to be anything fancy. Something like this will do: "I will sleep restfully, and awaken refreshed, alert and focused." I usually say it three times to myself before going to sleep. And 99 times out of a hundred, it works! I wake up refreshed and ready to go in the morning, with no morning grogginess or mental dullness. It's called making a mental resolution. And the mind will obey once you begin regaining control of it.
Try it sometime. You might just surprise yourself.
"The gift of truth exceeds all other gifts" — Dhammapada, v. 354 Craving XXIV