Has anyone else experienced Mirt stopping working for sleep?

I’ve been taking Mirt for about 15 months, initially on 15mg. It literally saved my life at a very dark time - I suffer from extreme episodic bouts of insomnia that then cause panic attacks and crippling anxiety through sleep deprivation. At the time it was the only thing that worked for my sleep. I slowly tapered down over the last year to 3mg and then had a relapse and now after a summer filled with more and more episodes of insomnia for one reason or another (not to do with the meds) I’m now on 18mg. I’ve noticed over the last few weeks that Mirt is no longer having the sedating effect on me that it used to, and wondered if anyone else has experienced this. I’m fully aware that it’s supposed to be more sedating at lower doses, but I can’t seem to get down low enough on a slow taper without having something else happen in my life that causes insomnia and the subsequent crippling anxiety. I’m at a bit of a loss with what to do now - if it’s not helping me during those episodic (but severe) nights of insomnia anymore I’m not really sure why I’m on it. Recently I’ve been having to rely on taking a small (2mg) dose of valium on the nights when it’s really bad - again I’m fully aware of the risks with that and I’m only taking one or two 2mg tablets a month, if that. The last thing I need is a benzo addiction. Has anyone else experienced Mirt stop working for their sleep after a while?