Pulling down on the joystick while in the air has no effect whatsoever. There is no "down", there is only freefall. Until I realized this, I used to blow myself up with bombs a lot too. Similarly, although there is an up, you don't need to go up to become airborne; as soon as you step off a platform, you're flying. Sometimes you want to go up first, to be sure, but more often than not, you're just wasting time (note the delay when pushing up off a platform.)