I've had severe turbulence twice in 37 years of flying.
never extreme turbulence.
now, an encounter with any turbulence MAY cause a pilot to over control the plane and cause some problems
but the big question to the original poster is this...was your seat belt as tight as it could possibly go? if you hit any turbulence and you are not strapped in tight, it will feel MUCH worse than it actually is.
so, first thing, fasten seat belt as tight as possible, your ride will be better for it.
also a DC9 was flipped over following a heavy jet due to wake turbulence