Yes! I can completely relate. In fact, I'm feeling it right now. For me it has no apparent cause. Things are looking good right now, yet, it's there and I don't know why. I think it's called "free floating" anxiety. My theory is there's a fear message being sent from my lizard brain, the limbic part, and the adult brain, the prefrontal cortex, can't seem to calm it down.
Other than a klonopin, I've found certain things can help.
Deep breathing, with a CD, guided is best for me.
CBT, write down all the good, reassuring things going on in my life.
Exercise, exercise, exercise.
Meditation, feel it, don't fight it, let it go away.
Focus on one activity at a time.
Distractions are helpful.
It can't hurt me. And it will fade. I hope this helps.