You'd die if that happened :p. Or you'd go in some random direction..
The principle is exactly the same; being moved by the force radius of the weapon. If an opponent shoots at a high angle (greater than, say, 80*) and the ground, it will have the same effect as your weapon would, but it would be somewhat harder to control the direction in which you fly away across the landscape.
As for taking damage, you take damage from any weapon unless self-damage is off or TDM or zombies has messed up all the weapons.