A dream can leave the feeling of a memory without supplying a past.

A dream can leave residue with nothing attached. You wake with the weight of having lost something or wronged someone, and there is no event to attach it to and no way to resolve it, because nothing happened. The feeling is real and it is not evidence of anything.

When a mood arrives that way, name it as unattached rather than searching for its cause in your actual life. The search will find something plausible and it will probably be wrong. Give it a few hours before you let it inform any decision.