I haven't been diagnosed with OCD but I really think I have it. These kinds of thought spirals always get worse for me at night too and make it so hard to sleep. Reading usually helps me if it's an engaging enough book to capture my whole mind and redirect the mental traffic. Looking outside, especially if it's a clear enough night to see the stars, also helps get my mind on something else. But a warning, because it can come to a point of contemplating eternity and still leave me wide-eyed for most of the night. Still, it's better than the thought spirals that put me into a black hole of depression.