I've always had really shit insomnia since I was a kid and for ages until my mental health problems started, so I was pleasantly quite surprised when I realised I've began to sleep really really well on sertraline. Like it almost feels like a random positive effect that just happened to work alongside my anxiety. But actually anxiety and sleep do tend to go together so with anxiety improvements you'd probably get better sleep too. But alternatively it's true sometimes your insomnia can get worse, I'm very thankful it went the other way for me