When I first started meditating, if I tried doing it while lying down I would usually start to fall asleep. Meditation is not the same as sleep, so you'll want to avoid sleeping when you do it. That said, if you end up sleeping during meditation, then it prob means that's what your body means.
The most simple meditation is a breathing meditation to clear the mind and return to baseline. Do this sitting up. You don't need to be all cross legged, you can sit in a chair or however is comfortable.
Close your eyes. Breathe normally and through your nose only. Draw your attention to the breath, specifically how it feels cool on the tip of your nose when you inhale, and how it's warm when you exhale. Keep focusing on this. If your thoughts wander then gently bring yourself back to your centre of focus, which is that sensation of air on the opening of your nose. Don't punish yourself if your thoughts wander, just be relaxed about it. Bring yourself back.
If thoughts come to mind, then gently allow them to flow through you without grasping them. Keep bringing yourself back to focus. With practice, this meditation allows you to experience emptiness. The mind turns off completely yet you are not unconscious when it does, and when the meditation is over you feel refreshed and grounded.
This meditation teaches you that you are not your mind, and that you don't need to identify with your mind's thought-stream. It is something you can disengage from, or simply observe with cool detachment. And it's a meditation you can achieve for just 10 minutes a day.
