Deep Sleep: Why It’s Essential for Your Health

For this feature, we interviewed our Mind & Mental Health expert, Heide Ziegenbein from Lanserhof Sylt, who shared her expertise in the fields of resilience, hypnosis, and trauma.

1. What is non-REM and REM sleep? What is deep sleep, and when does it occur?

Non-REM sleep (NREM) and REM sleep (Rapid Eye Movement sleep) are the two main phases of sleep, which alternate throughout the night:

Non-REM Sleep

Non-REM sleep is divided into three stages:
Stage 1: Light sleep from which you can be easily awakened.
Stage 2: The body relaxes further – heart rate and body temperature drop slightly.
Stage 3: Deep sleep – a very restorative phase where the body performs most of its repair work (e.g. muscle regeneration, immune support).

REM Sleep

REM sleep begins around 90 minutes after falling asleep. The brain becomes more active – similar to when you’re awake – and dreaming occurs. It’s important for memory, emotional processing, and learning.

We cycle through NREM and REM sleep several times a night. Both are important, but deep NREM sleep is especially essential for physical recovery, while REM sleep supports brain function.

2. What are the benefits of deep sleep for the immune system?

During deep sleep, your body increases the production of cytokines – proteins that regulate immune responses. Some are pro-inflammatory and help fight infection or aid in recovery from stress or injury.

Deep sleep also boosts T-cell activity and improves their binding ability to pathogens.

Additionally, cortisol levels drop during deep sleep – allowing your immune system to function more effectively.

In short: Deep sleep supports tissue repair, reduces inflammation, and activates the glymphatic system to clear waste from the brain – all crucial for immune health.

3. How does deep sleep restore energy in the body?

Deep sleep is like charging your body overnight.

The body produces ATP (adenosine triphosphate), your cells’ main energy source. Mitochondria also work more efficiently to replenish energy.

It also helps with muscle repair and activates the glymphatic system for mental refreshment.

4. How does deep sleep repair tissues?

Deep sleep is like your body’s repair shop.

The pituitary gland releases human growth hormone (HGH), stimulating cell growth, tissue repair, and muscle regeneration.

It also regulates inflammation – reducing harmful responses and promoting healing.

Lack of deep sleep leads to increased inflammation – a risk factor for many diseases.

5. Why does a regular sleep schedule promote deep sleep?

The brain loves rhythm.

A consistent sleep time synchronises your internal clock, helping with melatonin release and quicker transition into deep sleep.

Sleep runs in ~90-minute cycles. A regular bedtime improves the quality of each cycle.

Irregular schedules can reduce time spent in Stage 3 deep sleep.

6. How can an optimised sleep environment support deep sleep?

Deep sleep thrives in a quiet, cool, dark, and calm environment.

Examples:
– Darkness: Blackout curtains or eye mask
– Cool room: 15–19°C is ideal
– Noise control: Earplugs or white noise
– Comfort: Supportive mattress and breathable bedding
– Tech-free: Avoid screens before bed
– Relaxing atmosphere: Soft light, lavender scent, or calming sounds