Our minds are naturally really good at envisioning worst case scenarios and worrying about problems before they've ever happened. And since it comes from your own head, of course it'll feel like truth. But the actual probability of something going exactly the way you think it will is very low. Next time you keep yourself awake with nightmares conjured up by your fear, try to think of it like this, "I cannot predict the future, much less in the state I'm in right now," and trust that the reality of things will be much more indifferent (and maybe even much kinder) to you. than you are to yourself.