Our primitive ancestors evolved well equipped to live in the wild.  Much of our neurology and physiology makes complete sense in this context, because the few hundred thousand years for which we have been civilised is an eye blink in evolutionary terms, so we have come into this technological 21st century perfectly equipped to live on the wild plains of Africa.

However short of sleep they were, it was important for our ancestors to stay conscious if they were in danger, so one of the effects of adrenaline is to postpone the need for sleep.  Of course, if we are in physical danger, that mechanism can still be appropriate today. 

Unfortunately for us our ancestors did not need to evolve any mechanism to deal with long term stress, because if they were stressed, then within minutes they were going to be either victorious or dead.  In the world in which we humans evolved, long term stress did not exist. 

So what happens when we go to bed still stressed from the day?  The adrenaline in our system effectively prevents us from sleeping. 

This is made worse because the high levels of adrenaline in our system is likely to trigger further thoughts about the problem as we lie there.  This starts the further release of more adrenaline into the blood stream, because the primitive parts of the brain near the brain stem, which control our emotions, have no way to tell the difference between what we are seeing and hearing in reality, and what we are picturing in our minds, or thinking about. 

So as we imagine or think about what is troubling us (i.e. worry) we experience the same emotional response we would experience if it were really happening, right now!  So worrying thoughts will make it difficult to fall asleep, a problem called onset insomnia.

Some find it easy to drop off to sleep in the first place, but then experience broken sleep.  If we are falling asleep, or sleeping lightly, when we start thinking or dreaming about what has been troubling us, the release of adrenaline means we wake again, fully alert.  This happens whether we are remembering something real, or just imagining something that might happen. 

So most insomnia actually has the same structure as anxiety.  Sometimes an anxious person may deliberately keep him/herself busy during the day, to avoid thinking about the problems, and those thoughts then surface when they try to sleep. 

It is commonplace for the beginning of real relief from insomnia to be noticed within the first few treatment sessions.  It is important, if these changes are to become permanent, to do the further work to identify the thought patterns causing the problem, so that these can be addressed, with the intention that the person can become free from insomnia for good.