When we don’t sleep well, it leads to chronic nervous system ‘hyperarousal’ keeping us unable to wind back down properly, which is how the brain recovers or bounces back. Chronic poor sleep and insomnia is associated with a 24-hour increase of corticotropin and cortisol secretion (stress hormones), increased inflammatory markers, disrupted brain calming chemicals (such as our calming brain chemical called GABA). Insomnia is also associated with HPA axis dysfunction, our stress regulation system. This means we don’t cope with stress as well when sleep is less than optimal and are more vulnerable to toxic stress.
Another brain network called the RAS (reticular activating system) which is in charge of wakefulness but should become quiet during sleep, can become hypervigilant at the wrong time (eg. at nighttime) when you are trying to sleep. This RAS dysfunction is associated with many chronic health conditions including ADD/ADHD & depression.
The thalamus, which is like the brain’s pacemaker and decides how we filter information, is also impacted by poor sleep. This explains why when we don’t sleep well, we can feel scattered and have trouble focusing and have poorer cognitive (thinking) ability.