Fear and Worry
They're directly related, fear and worry. If something is plaguing your mind, consuming your thoughts, you're both afraid of it, and worried about the outcome. These two work in tandem and become difficult to overcome.
You won't find the answer to getting rid of them here. Sorry. I struggle with them too. There are a couple practices that may help though. You can look back and see how many worries were valid (not many), or try to focus on a positive outcome, but neither method is great.
What I do find is that living life with people you care about can really help. Sharing a funny story, laughing with friends, truly living can hold worry at bay. Maybe it's because you begin to realize how blessed you truly are, or maybe you see others enjoying life without the burden of worry. Either way, get out of your head, stop thinking so much, and start living.