Unknown feeling

I've never been good at identifying emotions. The only emotions I can ever think of are sad, mad, and happy.

Well, I have this feeling that's been haunting me for the past few days. I can't put my finger on what it's called. It's like a very deep sense of loss, though I haven't lost anything. It's kind of an anxious pain that moves like a wave from my stomach to my heart. I guess you could describe it as butterflies. But it doesn't make any sense. There's nothing that should be making me feel like this.

And it's crippling. I keep hoping that it will pass, hoping that I can identify the damn thing so I can recognize it and move on... but I just don't understand.

Help?