@Ilias-Ant
Perhaps there is a lot of serotonin coming from your gut bacteria from having too much gut bacteria. You may want to minimize intake of soluble fiber to keep the growth of gut bacteria in check.
At the same time, you may want to check if your lungs are clear, and if not you can take some supplements like NAC to help clear phlegm so that your lungs have good gas exchange and are able to breathe in oxygen and breathe out CO2 easily, as the proper flow of gas into and out of the lungs enables serotonin to be deactivated. Having a source of negative ions to breathe in by sleeping by the waterfalls or by the sea will help also, or alternatively a negative ion generator can be used in their place.
Also, if you are able to produce more CO2 than lactic acid by having good mitochondrial respiration that produces plenty of CO2, your platelets will be able to carry serotonin with the CO2 to the lungs where serotonin can be deactivated. With less free serotonin that gets into your brain, you will have less chance of insomnia.
Use of cyproheptadine will also help, but it won't help when there is simply too much free serotonin in your system.