As we glide down into slow wave sleep, some obvious things occur to facets of the stress-response system. For starters, the sympathetic nervous system shuts down, in favor of that calm, vegetative parasympathetic nervous system. In addition, glucocorticoid levels go down.
In contrast, during REM, as you’re mobilizing all that energy to generate that outlandish dream imagery and to move your eyes rapidly, glucocorticoid secretion and the sympathetic nervous system rev up again. But given that most of what counts as a good night’s sleep consists of slow wave sleep, sleep is predominantly a time when the stress-response is turned off.
About an hour before you wake up, levels of CRH, ACTH, and glucocorticoids begin to rise. (CRH is the hypothalamic hormone that gets the pituitary to release ACTH in order to trigger adrenal release of glucocorticoids).
This is not just because merely rousing from slumber is a mini-stressor, requiring mobilization of some energy, but because those rising stress hormone levels play a role in terminating sleep.
So deprive yourself of sleep, and the sleep-induced decline in the levels of those stress hormones doesn’t occur. They rise instead.
Lots of stress can potentially lead to little sleep. But stress not only can decrease the total amount of sleep but can compromise the quality of whatever sleep you do manage to get.
For example, when CRH infusion decreases the total amount of sleep, it’s predominantly due to a decrease in slow wave sleep, exactly the type of sleep you need for energy restoration. Instead, your sleep is dominated by more shallow sleep stages, meaning you wake up more easily, fragmented sleep.
Moreover, when you do manage to get some slow wave sleep, you don’t even get the normal benefits from it.
When slow wave sleep is ideal, really restoring those energy stores, there’s a characteristic pattern in what is called the delta power range that can be detected on an EEG (electroencephalogram) recording.
When people are stressed presleep, they get less of that helpful sleep pattern during slow wave sleep.
We have the potential for some real problems here, insofar as lack of sleep or poor-quality sleep activates the stress-response, and an activated stress-response makes for less sleep or lower-quality sleep. Each feeds on the other.
If you go to sleep thinking that not only will you be woken up earlier than you would like, but at an unpredictable time? Where any minute could be your last minute of sleep for the night? It’s quite possible that stress hormone levels will be elevated throughout the night, in nervous anticipation of that wake-up call.
As we’ve seen, with an elevated stress-response during sleep, the quality of the sleep is going to be compromised.
Thus, there is a hierarchy as to what counts as miserable sleep. Continuous, uninterrupted sleep, but too little of it, deadline looming, go to sleep late, get up early, not good. Even worse is too little sleep that is fragmented.
This teaches us a lot about what counts as good sleep and how stress can prevent it.
When it comes to what makes for psychological stress, a lack of predictability and control are at the top of the list of things you want to avoid.
Taken from Sapolsky, Robert M.. Why Zebras Don't Get Ulcers