I have not faced that exact situation, where the type of thinking you described happens for any and all situations at hand; but, I have faced that situation across my life and can think of a few scenarios at the moment. For example, if my girlfriend is out in town with her friends and alcohol is involved, I worry in general and then there are moments when I do contend with worst case scenarios.<p>I don't think that computing worst case scenarios is devoid of light, but it can be rough.<p>What I like to do in these situations is to pray to God. I like to seek refuge at God, from Satan the rejected. I believe God is the Eternal Refuge. I seek refuge as many times as I feel the need to. I believe imploring God is a form of worship, and worshiping God is good, therefore I continuously implore for things, including refuge.<p>Hope it helps, and that you have a blessed night.
I feel this way at times as well, a therapist can help with techniques like Cognitive Behavioral Therapy. Also check out Ryan Holiday's podcast... they often help put things in perspective. For some people mediation helps, it doesn't work for me but I have never had the discipline to consistently implement it. I can't say I 100% avoid such thought patterns but I am better at avoiding them or at the very least shutting them down quickly now than I was 2 years ago.
I remember that hope is available to those who need it. "There is hope, even when your brain tells you there isn't."<p>Essentially every negative situation has a positive side to it. The trick may be to train your brain to identify it, and then you may gravitate toward thinking about it more once you have learned to see it.