Head,
That sucks pal. No one should die while enjoying their sport.
Fred,
Knockdowns happen from a myriad of reasons and/or conditions.
The good news, they are few & far-in-between.
I got somewhat knocked down twice but, the difference was not from wind/waves but from two Microbursts.
These were discovered in the early Seventies with the advent of Doppler Radar. They then were able to determine why planes taking off & landing suddenly crashed. Now, airports check Doppler radar first.
Once while under sail & once while motor-sailing & a lone sailor, it happened to me but, there are no witnesses or documented proof that they ever happened but...............they did.
Both times, my boat was happy & moving forward albeit at an extreme angle. It was only when the rub rail & cockpit started flooding that really got my attention. When water rushes into your cockpit yea, it WILL get your attention.
As for knockdowns, stay away from them. When conditions get spirited & you first question your stability, first of all, shorten sail, maybe motor, maybe change course or, all of the above. Never get caught by surprise man. Remember the adage of the prudent navigator............
Boating is dynamic & in this sense, conditions forever change. Just make sure you also change in time.
CR