I've never experienced a knockdown as a result of waves, and would prefer not to. I have cruised my 22' trailer sailer quite a bit and because of that purposely sailed in thunderstorms on protected waters to gain experience handling bad weather and have had the mast in the water several times (I replaced all of the rigging on the boat before doing this). What got me in those circumstances were wind shifts associated with gusts. They just blew me on my side and held me there until the gust slacked.
The first time it was kind of tense, but the boat righted quickly. If there is any chance of bad weather I always batten down like a hurricane is coming, everything has to be stowed. I lock all the lockers and hatches, and don't open them once the weather hits. Life jackets and jacklines are used. The worst thing that ever happend was one May when we we playing in a thunderstorm. I was on the low side and the water was like ice. One of my friends said I was a lovely shade of blue.
Playing in the storms was a great help because when I've been in places where there was no land in sight and a squalls hit I was able to deal with them comfortable, because I'd already experienced bad weather. Once the boat was under control I would try diferent tactics to see what I could do with them. I must confess that there does seem to be a big difference of wind power in protected waters and open waters. The weather service and locals with anenometers would say there were 30-40 MPH winds with gusts in the 50's on the lakes but when I've been in open waters 20-30 with gusts in the 40's (according to the weather service) was a lot more intense. It must have something to do with turbulence from the trees and shore clutter on lakes vs nothing to disturb the wind over a longer fetch on more open water, but that is a pure guess on my part. The waves were of course much bigger, but we are only talking 6 or 8 feet with a 10 to 20 foot period in open water.
I don't plan on purposely trying this where big waves are involved. There is just too much risk. Actually I don't go out asking for it anymore, I learned what I needed to and now I just use the lessons when required.