Having delusions, but only delusions that one wishes were true (that you took a trip you dreamed of, played with your children a lot when actually you never once did, etc.)

In the case I'm talking about it seems to start out as a lie told to others or oneself, then slowly convince the person to the point that they believe it. In some cases, the sufferer is easily corrected ("Oh, we never went on that trip?") and in others will not budge regardless of the evidence.

What disorders could this be a symptom of?