It's a sudden, embarrassing slice of silence. A senior moment. Most of us begin noticing these awkward interludes in our 50s. By 70, some of us will avoid talking altogether, not an altogether unvirtuous act. I even know younger people that have the same problem. I like to call it BRAIN BLOAT.
Brain bloat is the result of too much stuff in the head. That's why it usually takes 50 or 60 years of input before the forgetful symptoms begin manifesting. After all those years of cramming stuff into your head, it finally begins overflowing like a water glass unable to hold another drop without shedding something already there.