When I was ten, I went to Water World for a friend's birthday party. We went to Thunder Bay (you know, that huge loving wave pool that blasts a huge loving wave at you every so often) to hang out for a while, not swim. After a bit he decided to go in the water because he said, "It looks so fun to get knocked over by the wave," so I went with him. The unfortunate part about Thunder Bay is that there's a stuffload of people on inner tubes right near the wave generators, so they fly out with the wave and collide with you if you're not watching them carefully.
Sure enough, I wasn't being too attentive and didn't notice the large man on an inner tube hurling at my face. You can probably imagine what happened from then. Why was this the scariest moment of my life? Because when he hit me, impulsively I inhaled from shock and surprise - after my head was under the water. So now I just swallowed a mouthful of water that contains who-knows-what, my nose felt like it was broken from the impact (which it wasn't completely broken, just cracked slightly), and I skinned both my knees on the bottom of the pool. Not to mention that I couldn't surface because the loving inner tubers kept coming over me in a seemingly endless wave of hurt. In other words, I was hit multiple times by people on tubes.
The feeling of drowning has to be one of the absolute worst feelings ever.
