Insomnia - The Fight or Flight Branch of the Nervous System

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Under normal conditions, the sympathetic nervous system will occasionally switch on in response to a threat or an acute stresser. It's because of this that we commonly label it as your body's aggravating, or fight or flight branch of the nervous system. And like a car engine that is put in neutral, the fight or flight branches should not be reved with foot to the floor for long, chronic periods of time. But insomnia sufferers suffer from chronically high levels of these physiological reactions when they are trying to fall asleep.

Today’s episode focuses on changes within the bodies of people suffering from insomnia. Almost all forms of chronic insomnia come with a significant psychological component, namely emotional distress and anxiety. This starts a Rolodex of anxiety spinning once you turn off the lights. This leads to rumination and catastrophizing, which will thwart any hopes of a good night’s sleep.

Since psychological stress is one of the principal triggers of chronic primary insomnia, researchers went in search of the underlying biological cause. We found two culprits.

First was an overactive state of the sympathetic nervous system. Under normal circumstances, it will occasionally switch on in response to a threat, kicking off a cascade response which increases your heart rate, blood flow, and metabolic rate. However, a chronic elevated flight or flight state, as occurs in insomniacs, has damaging biological consequences. A racing heart and raised metabolic rate lead to a raised core body temperature, when exactly the opposite is necessary for good sleep.

Second was the discovery of an excessive amount of activity in the adrenal cortisol-producing system (called the HPA axis) in insomniacs. When you experience a chronic state of stress, worry, and anxiety, that adrenal stress HPA axis instigates a chain of command response, resulting in the release of the wake-promoting hormone called cortisol. In good healthy sleepers, cortisol levels normally hit their lowest levels right at the point they’re falling asleep.

In insomnia patients, cortisol levels do start falling early in the evening. But then, they spike back up right at the point of bedtime. Later in the middle of the night, we also see cortisol levels once again spike in insomnia patients. These two spikes seem to overlap with the two main flavors of insomnia: sleep-onset and sleep-maintenance.

Please note that Matt is not a medical doctor, and none of the content in this podcast should be considered medical advice in any way, shape, or form, nor prescriptive in any way.

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