"Fear is the first enemy of a person of Knowledge."
don Miguel Ruiz
Fear normally stems from attachment. When we are attached to something, we don't want to lose it. That desire to keep things manifests itself as fear.
What are you so attached to that you don't think you could bear to be without it? Examine that, and you may begin to get a sense of the origin of your fear.
Once you've done that, you need to get that NOTHING and I mean NOTHING is ever
yours anyway. One of the biggest fears for most people is the fear of death. Usually NOT their own. But the fear of the death of a loved one; a parent, a sibling, a spouse, a lover, a child. We fear this because we feel that we will "lose" this person, as if somehow they were ever "ours" to begin with. But sometimes, fear is of a more mundane variety: fear of losing a job, fear of being in an "unsafe" environment...
I don't need to tell you that Fear has no place in our lives - you seem to get that already. There are a lot of books out there on the subject of Fear. Whence it comes, it's impact on us and how to relinquish it.
Simply acknowledging that you are living in fear is a tremendous step towards letting it go. Congratulations!
Here are a couple of books that I recommend:
"The Four Agreements", don Miguel Ruiz
"Places that Scare You", Pema Chodron
I'm sure others here will have alternate resources.
Good luck!