Have you ever been stressed, but didn't know the cause?

For the past few nights, whenever I try to fall asleep, I just end up lying there for hours because I feel stressed.
Nothing is really wrong..
My life is awesome right now. Or, at least as awesome as it can be.
I am very happy, I just feel stressed.
Maybe I’m not? Maybe I’m just broken.

Has this ever happened to you?
What kind of impact did it have on you?
What did you do to try to help it?
Did you find out what was causing it?