I have gone whitewater rafting and experienced a river flow from placid to panic --often rather quickly. Mostly, it is just fun, a wild, adrenaline pumping, rolling wet good time. I have had a few dreams (nightmares?) where I am on the water and realize too late I have reached the point of no return and, no matter what, I am going over. It is like that dreaded falling dream but with and added twist. Luckily, I normally wake up before I hit bottom. Needless to say, I wouldn't try this at home.