I've had thoughts and stories and fantasies running through my head as well. For obvious reasons, I never know they have turned into delusions until after the fact. What differentiates them for me is that when I believe one of my fantasies will come true as opposed to believing that they could come true, I have crossed the line into delusion. That would seem obvious to someone who has never had psychotic delusions. The truth is that it is harder for us to tell that it is happening to us.