Novices ask the question whenever the wind begins to blow and the boat is moving nicely.
It is a normal fear I suppose whenever your seat and feet don't line up with the horizon. They may sound reassured but white knuckles on the rail betray continued anxiety. The real truth is that it's possible for any boat with any ballast to experience a knockdown. Mine never has and probably won't and is designed to pop right up if it should ever happen. When life knocks us down we give thanks to whomever for the ballast that sets us right.