sometimes i dream that ive had a conversation with someone and when i think about it afterwards im utterly convinced the conversation was real. i dont remember dreaming it but thats the only explanation i can come up with. other times i do have conversations and have no memory whatsoever of them either because i was severely depressed at the time or severely anxious. in your case though i would agree with others that it could be the amount of medication you re on.
take care
biiv