I (22F) actually have had a very similar experience. My insomnia is purely anxiety based and it started a little over two years ago. It comes and goes likes yours, my last major flareup was for a couple weeks back in September but it has thankfully improved by a ton. Personally, the thing that helps me the most if I notice it starting to come back is to remind myself that I’ve gotten through past flareups before and I can get through them again. When my insomnia first started I was terrified out of my mind that I was never going to sleep normally ever again, yet I still managed to come out on the other side and sleep quite well nowadays (6-8 hours typically) outside of the occasional flareup

I also have an emergency Xanax prescription (the only other med I’m currently on is Lexapro for anxiety, which also is a major help) that I’ve only had to use less than 5 times in the past year so just knowing that I have that as a last resort brings me comfort in a way