Sorry about your friend, white water rafting can be fun but never forget the River is not your friend. I was never comfortable enough to kayak, but my wife did it.
Holes can be scary, Class IV not so bad, Class V and up can actually hold a boat in place and not let it go if you dont hit right. Its almost like a standing wave, it pushes you right back into the rock. Some Hole's are called Keepers, they suck ya down and then you can get caught under the rock and the force of the water wont let you up
During training I got tossed into a hole when I screwed up. We were using "funyaks" kind of inflatable kayaks but more like inflatable canoes. early April, still some snow on the ground. Took my hat off and stuffed down inside my wetsuit and zipped it up, fastened up my PFD, and tightened up my croakie for my glasses and proceeded to row down the river. First rapid we come to is Mike's Hole. as you come down you cant see the hole or the rock but there is a slight bump in the water so you have an idea where not to go and steer around it. Each person was following the last person through the rapid, I was about 2nd from the end. I saw the person in front of me make it through so I took that line, got to close and the wave just popped my boat straight up in the air and I got dumped. It sucked me down, bounced me off the bottom a couple of times and then spit me out. All I had to remember was keep my feet up in front of me and paddle to the shore. I lost my glasses and my hat was retrieved floating down river ahead of me.