I've had a number of existentially-induced insomniac "sessions" of this. Although, it isn't quite a fear, per se.
As a child I had this dream in which I saw what happened that day and then everyone talking about me with nurses, making me seem to be mentally ill and everyone but me knowing it. So when my parents talked to my doctor what happened pretty often when I was younger, I wouldnt let them alone fearing that dream could be true. Made no sense at all, but I was maybe six.