I had high histamine as well, and follow a low histamine diet now.
I used to be unable to fall asleep if I had eaten the wrong type of food or had something with alcohol in it, which is very high in histamine. For me there 'definitely' a strong link between histamine and problematic sleep. (also between histamine and stomach/bowel problems).
I have always been someone to avoid alcohol almost 100%, even when I was young. But when I met my current partner it changed. He sometimes puts a lot of effort in creating a really nice dinner, and sometimes had some type of wine to go with it. I enjoyed that too, so that is where I started drinking alcohol sometimes. I quickly found out that wine (alcohol) causes me to be completely and utterly unable to sleep.
A doctor specialized in allergies, did not find any specific allergies but she did find I had high histamine, and advised a very strict low histamine diet.
Since then, I do not have insomnia anymore, unless I cheat and eat or drink something with lots of histamine in it. Alcohol is by far the worst one for me, it is really high in histamine.
A glass of wine will give instant insomnia. Its such a strong effect that I 'could' use it if I want to stay very awake for the whole night, I could eat histamine on purpose. It would work. (and would also have a bit too many downsides

)
But insomnia can also happen when I eat several types of food with lower amount in it, it just stacks up.
I do not know why I have high histamine, and why my body does not seem to be able to clear it very well. I have thought about the link with cortisol before, but so far there has not been any doctor who is willing to test or explore it.
I have found that nettle tea can sometimes help in a mild way, not much but I still use it. I read somewhere that nettle helps to break it down, like a natural antihistamine. So maybe you could try drinking several cups of a good nettle tea throughout the day, and some more in the evening. Maybe for 'at least' three days to give it a chance of lowering the histamine stack (that is what I call it now)
Its probably not strong enough, but it doesn't hurt to try I guess.
And I would definitely stay away from alcohol.