Let's say I've got a character on-screen, and he's tired. If he falls asleep, I lose the game. So I place a meter on one side of the screen that says "Awake-meter," and it begins fully charged at start of layout. Once "play" begins, I want the meter to constantly try to whittle itself away to an "empty" state. I'll lose if the meter is empty, so I arrange my game so that rapidly tapping the K and M keys puts a little "juice" back into the meter. If I'm not tapping the keys, the meter keeps going down. If I am tapping the keys, I can keep the meter up.
I don't know how to do that, and any advice would be appreciated. Thanks a lot!