Sleep is not linear. The sleep cycle architecture shifts across the night, with the final hours being disproportionately rich in REM sleep. Cutting 8 hours of sleep down to 6 (a 25% reduction) can result in losing 50-70% of your total REM sleep, which is vital for emotional and creative processing.

Contrary to the idea that sleep debt is irreversible, you can 'bank' sleep by sleeping more in the week leading up to a period of sleep deprivation. This creates a buffer that significantly lessens the subsequent cognitive and mental performance impairment.

Bryan Johnson suggests focusing on a single metric: pre-sleep resting heart rate. Lowering it through specific habits (like eating 4 hours before bed) improves sleep quality, which in turn boosts your prefrontal cortex, enhancing willpower and alleviating mental health issues.

A prerequisite for falling asleep is shutting down proprioception—your awareness of body position. Performing slow, deliberate eye movements (side-to-side, circles) can trick your vestibular system into this state, helping a racing mind fall asleep.

To combat a racing mind at night, spend five minutes writing down all thoughts and to-dos. This routine signals to your brain that it can 'forget' these items until morning, as they are safely recorded. It improves sleep quality and provides a clear, pre-made task list upon waking.

During REM sleep, the brain is in a unique state where the stress neurochemical noradrenaline is completely shut off. This allows the brain to reprocess difficult emotional experiences without the anxiety response, effectively stripping the painful charge from the memory itself.

Unlike sedatives like Ambien, a new class of medication (DORAs) works by dialing down the brain's wakefulness chemical (orexin). This allows for naturalistic sleep that is functionally beneficial, proven to increase the brain's cleansing of beta amyloid and tau protein, which are linked to Alzheimer's disease.

While sleep conserves energy by reducing metabolic rate by 10-15%, studies show that expert meditators can achieve a much deeper state of rest, lowering their energy expenditure by as much as 40%. This highlights meditation's potent and underappreciated role in energy restoration.

Catching up on sleep over the weekend can reduce cardiovascular disease risk by 20% compared to remaining sleep-deprived. However, this recovery doesn't extend to other critical systems; cognitive ability, immune function, and blood sugar regulation do not rebound.