What Is Sleep? | Phases, Circadian Rhythm & Why It Matters

Aidan
Nov 3
2 min read

What Is Sleep?

Sleep might feel like simply “switching off,” but it is one of the most important processes for health. While we sleep, the body repairs itself, the brain clears waste, and memories are organised. Without enough quality sleep, energy, focus, and even long-term health can be affected.

A drawing of a dreamcatcher. Beneath which is the definition of the noun "Dream" as "A series of thoughts, images, and sensations occurring in a person's mind during sleep."
This is followed by a quote from Ursula K. Le Guin "I am living in a nightmare, from which from time to time I wake in sleep."

The Phases of Sleep

Sleep is not one single state, we move through stages several times a night in cycles of around 90 minutes. Sleep Foundation

Light sleep (N1 & N2): The transition into sleep. Muscles relax, heart rate slows, and body temperature drops.
Deep sleep (N3): The most restorative stage. Tissue repair, growth hormone release, and immune strengthening happen here.
REM sleep: Linked to vivid dreams. Brain activity rises, supporting memory and emotional processing.

It’s normal to wake briefly through the night, these short awakenings are part of healthy sleep. Researchers show this cycle in a hypnogram, which maps how we move between sleep stages.

Circadian Rhythm: Your Body Clock

Sleep is also guided by the circadian rhythm, a natural 24-hour “clock” that helps the body know when to be awake and when to rest. HelpGuide

Light exposure: Daylight helps us feel alert. Artificial light at night, especially from screens, can make it harder to fall asleep.
Body temperature: Our core temperature naturally drops at night, helping signal sleep.

When circadian rhythms are disrupted (e.g. shift work, jet lag), sleep quality often declines.

Physical Benefits of Sleep

During sleep, the body restores itself in ways we can’t replicate while awake:

Hormone release: Growth hormone supports repair and development.
Immune strength: Sleep boosts immune function and regulates inflammation.
Heart & metabolism: Blood pressure lowers, and the body manages blood sugar and appetite hormones.

Consistently poor sleep can make it harder for the body to regulate these systems, increasing long-term health risks.

Mental Benefits of Sleep

Sleep also helps the brain reset.

The glymphatic system “washes out” waste products such as amyloid-β, especially during deep sleep. NIH
This process reduces inflammation and helps protect against cognitive decline.
Sleep strengthens focus, learning, and problem-solving skills for the next day.

Why Do We Dream?

Most dreams occur in REM sleep. While their purpose is still debated, research suggests they may:

Help the brain sort memories
Allow us to process emotions
Spark creativity by combining information in new ways

Dreams are a sign of the brain actively working, even while we rest.

Final Thoughts

Sleep is much more than “rest.” It is a carefully designed process that restores both body and mind. From deep sleep that repairs tissue, to dreams that process memories, each phase plays a vital role.

If you’re struggling with poor sleep, difficulty switching off, or nighttime worry, support is available. Speaking to a therapist can help you build healthier sleep habits and reduce the anxiety that often keeps people awake.