Updated: Nov 13, 2019
The reason for sleep is to repair and it’s important for general health and wellbeing.
If you want to get technical about the hormones and where they come from, read this. If not, skip to the next paragraph. The hypothalamus, midbrain and brain stem produce GABA and adenosine to relax us, these are incredibly important for the falling asleep part and to generally feel relaxed; the pineal gland produces melatonin (sleep hormone which helps regulate your body temperature, blood pressure and hormone levels), then the thalamus and cerebral cortex act together to create dreams (4).
While we sleep, the amygdala (in our brain) increases activity, which suggests a lot of processing emotions and “sorting through” stimulus happens. If you don't know, there are different stages of sleep, the length and pattern of these stages is important for us to feel restored when we wake up. There are three or four stages of non-REM (non-rapid eye movement) sleep where our bodies slow and rest, and then there’s REM (rapid eye movement - super inventive with the names, right?) sleep where we have vivid dreams. We cycle through the stages throughout the night, spending only about 2 hours actually dreaming (4). Slow wave sleep (SWS) encompasses non-REM stages 3 and 4, and this is where it is suggested most recovery occurs (5).
How stress disrupts sleep is largely based on the Hypothalamus-Pituitary-Adrenal (HPA) axis and the subtle changes in dominance between the sympathetic nervous system and the parasympathetic nervous system.
The parasympathetic nervous system (PNS) controls homeostasis and the body at rest and is responsible for the body's "rest and digest" function. The sympathetic nervous system (SNS) controls the body's responses to a perceived threat and is responsible for the "fight or flight" response.
Stress impacts the circadian rhythm due to the higher levels of cortisol and epinephrine (adrenaline) that are activated by catecholamines (a group of neurotransmitters) released immediately after exposure to stressors (2). Glucocorticoids (such as cortisol) and epinephrine, released from the adrenal gland, can act as synchronizers of circadian tissue clocks, meaning that changes in their levels or release times can alter the circadian rhythm.
Because of this change in chemical messengers, one can experience insomnia, more frequent waking during the night, bad dreams, and unrefreshing sleep. These two hormones (cortisol and epinephrine) oppose melatonin and other relaxing hormones to control the sleep cycle. As cortisol is high, melatonin is low, and vice versa.
A change in these hormones levels, such as increased cortisol for a longer period of time, impacts the strength of the effect and timing of release of melatonin, impacting the sleep pattern.
When you don't get the right amount of Slow Wave Sleep vs REM