I have only encountered what I would describe as severe turbulence in a jet transport once in 20+yrs of flying and I do not wish to encounter it again: it was a fight just to keep the brown and blue the right way round, nothing else was controllable.
That would be it, only managed to encounter such twice in my 42 year, 21,000 hour career. One when as co-pilot in a Jet Commander* when complete control was lost at FL 390, when our radar failed traversing a line of thunderstorms, recovering around 12,000 feet when we were thrown out of the side of the storm inverted.
Second time was due to CAT in a 727. I lost 4,000 feet before I could regain complete control of the aircraft. I had some cabin crew injuries then, as there was no warnings at all. It was smooth as could be in total VMC and we ran into a brick wall**. Well it seemed like it and as you said, it was all I could do to keep the greasy side down, barely.
* Some may criticize Jet Commanders, but one thing about them, they were built like brick
houses, one tough bird. I should know.
** The guy in the co-pilot's seat happened to be looking at the INS wind read out and we went from a 100 kt plus tail wind to a 90 plus kt head wind within a minute.
By the way, you've been flying for a little over 20 years. Well using my average, you've got one more coming.
Just kidding, smooth skies my friend.