How can I keep myself from falling asleep after about five minutes of meditation?
First of all, before you start meditating please breathe in deeply a few times. With each breath, try to feel that a stream of energy is entering into you. Then try to feel that you are breathing in through different parts of your body: your eyes, your ears, your forehead, your shoulders, the crown of your head and so on. Feel that each of these places is a door, and when you breathe in feel that you are opening this door. At that time, energy enters into you from the Universal Consciousness.
Then try to invoke the power aspect of the Supreme. Do not invoke peace or light; only try to bring forward divine power from within or bring it down from above. This divine power will make you feel that your body is burning with fever, although you are not actually running a temperature, and immediately you will feel energised. You can also imagine a blue-green forest or field, and feel that you are walking through it. Then, no matter how tired you are, you will feel energised. You can also pinch yourself as hard as possible, and try to feel that somebody else is pinching you. While you are pinching yourself, you have to know that it is your conscious self that is pinching your unconscious self. But you have to feel that another person is doing the pinching.
Another technique is to repeat the name of the Supreme as fast as possible. With tremendous concentration see how many times you can repeat "Supreme" with each breath. The power inside the repetition of this name will inundate your whole being and you are bound to feel a new flow of life-energy.
At meditation time always try to feel inside you a dynamic and progressive movement, but not an aggressive one. If there is a dynamic and progressive movement, then you cannot fall asleep. Inside you, feel that a train is speeding towards the destination. Feel that you yourself are an express train with only one destination. The driver of that train is constantly repeating God's name to derive energy, strength, stamina and all divine qualities. An express train stops only at the Final goal, the end of its journey; on the way it does not stop at all. Your goal will be to reach or achieve a profound meditation.