Insomnia is usually classified as a psychological condition, however I don't think that there is only one cause for it. Probably most cases aren't psychological.
In order to fall asleep you first need to accomplish a precursor state called relaxation. Everything that is going to stop you from being relaxed is going to stop you from falling asleep.
If your body is going to perceive any amount of danger it is not going to let you become unconscious, that would put you in a position where you wouldn't be able to react quick enough to that particular danger.
So it will keep you awake until you are safe and can relax, this makes things rather confusing because it is not like there is a bear in your bedroom every night that prevents you from relaxing.
Which is why some people reached to the conclusion that it must be something wrong with they're mind that is just preventing them from falling asleep, so they need spelling pills and therapy to manage it. And maybe some cases do, I am certainly in no position to diagnose.
However some of the stimulus that prevents you from relaxing can be from the inside of your body. Like an injury that affects the proper functioning of your body.
If your spine is deformed your body can't function wright, which is going to put you in a compromised position, your body is going to realise that and keep you awake.
A deformed spine is going to create several compromises in your body, it is going to affect the function of your nervous system, the function of your muscular system, the digestive system, the circulatory system etc.
It is not only the mind that can prevent you from falling asleep, since the mind it is just a function of the body, it is impossible to have a healthy mind in a sick body.
And when you have a population where the majority of people are walking around with untreated nervous system injuries, it is most likely that the obvious thing that is wrong with them, that you can see with your naked eyes from across the road, is what is causing their problems.
How are you supposed to be relaxed when you are walking around with all this compromises in your body. A bad posture is a major injury with potentially severe health consequence.
And insomnia could be another symptom of it. Bad posture has deeper implications than the negative esthetics implications and maybe some back pain later on in life.