My heart is pounding and our guide is yelling something I can't make out. I think he's telling me to paddle harder, so I bend over to put my oar into the water but, to my shock, the water is not there. Turns out, we are on the very crest of the wave, and our raft is almost vertical. Then we crash. The walls of white foam close all around me, and I can barely see, let alone breathe. When we finally come back to the surface, I feel like a sock must feel after spinning inside a washing machine.