spontaneous euphoria

Spontaneous Euphoria is the phenomenon when you're doing a seemingly normal routine, and all of a sudden you get hit by a random wave of extreme happiness. Studies show that the chance of spontaneous euphoria may increase greatly while doing something positively nostalgic.

*Your friend suddenly stops walking*

You: Hey, man, what's wrong?

Friend: *shakes his head* Oh, nothing, I just got a wave of spontaneous euphoria