Fun fact about me: I cry more when I'm happy versus sad. I've never understood why this happens. Update: I'm looking it up, and apparently it's our body's way of maintaining an emotional equilibrium. Tears, whether happy or sad, result in emotional arousal, which ultimately activates the hypothalamus and basal ganglia.
This has happened before! Like, it doesn't always happen, but I have had moments where I think "Wait... Deja Vu!" And then I think about when it was, until I finally remember that it was a dream the first time!