It's possible to practice meditation while walking, sitting, standing and lying down. However, unless you are experienced in meditation, it can be difficult to meditate while lying down without falling asleep. Meditating while lying down takes discipline to build up for five to 15 minutes every day before attempting it for long periods of time.
Lie flat on your back, on top of a yoga mat. Bend your knees. Bending your knees will help you to remain awake. If you fall asleep, your knees will relax, waking you up.
Keep your feet flat on the floor, and if necessary, turn your heels outward, slightly. Remain mindful of the position of your heels, which will help you to keep your feet straight and stay awake.
Align each of your hands in the "mudra" position, by touching your forefinger on each hand to your thumb. The "mudra," as well, demands mindfulness and alignment.
Listen to soothing music designed for the purpose of meditation to bring mental clarity.