Sometimes, while dreaming I will recognize and recall that I've had this dream before, maybe many many times...then I feel a sense of loss, like losing a friend

Sometimes, while dreaming I will recognize and recall that I've had this dream before, maybe many many times...then I feel a sense of loss, like losing a friend. A moment of de ja vu I guess. It is a weird feeling though, and I don't even know if I truly had the dream before, or if it is a false memory!!