Strange emotional reaction to a bad dream

I have never really been one to care about many people, until I met my girlfriend. We have only been dating for just under 3 months, but there are no words to describe how much I love her. About a week ago, I had a dream that she broke up with me for another person. This person is one of her best friend's boyfriend, and she is good friends with him as well. This doesn't sound like it's a very big deal, but for some reason I can't seem to shake it.

The morning after the dream was the worst morning I have ever been through. I was so sad that I actually felt sick to my stomach. When I went to school and starting doing things, everything seemed fine. But, whenever I am not doing anything, and I start thinking, my mind keeps going back to the dream and I get the same sick feeling. It is the worst feeling that I have ever felt in my life. I don't know what to do. I feel like an idiot, because this doesn't seem like it should bother anybody. I haven't told my girlfriend yet because I don't want to seem like an extremely jealous person, or someone that would like stalk her if she ever left me or something.

If you could give me any advice about how to make this feeling stop, I would really appreciate it.