How Sleep Works: Stages, Cycles and a Normal Night
The four sleep stages, the 90-minute cycle, the two systems that decide when you sleep, how needs change with age, and what a normal night looks like — including the wakings you forget.
Dr. Adekunle Ajisebutu, MD
Sleep physician · Founder and medical reviewer, Complete Sleep
Areas of specialization (as listed on MercyOne)
- Sleep medicine
- Critical care
Dr. Adekunle “Ade” Ajisebutu is a board-certified sleep physician at MercyOne East Village Sleep Medicine in Des Moines, Iowa, where his listed specialties are sleep medicine and critical care. He founded Complete Sleep to make sleep science easier to understand through evidence-informed, plain-language education, and he is the site’s medical reviewer.
Complete Sleep is written for readers who are tired, frustrated, or worried, and who deserve a straight explanation. Dr. Ajisebutu’s review checks that each article says what the evidence supports, flags what it does not, and is clear about when self-help stops and clinical care begins.
Credentials
- Board-certified in Sleep Medicine · stated on his MercyOne provider profile
Only credentials corroborated by a public source are listed here. Board certification in sleep medicine is stated on his MercyOne provider profile; further certifications will be added with the certifying body and year once confirmed.
Public provider profiles
Dr. Ajisebutu practises at MercyOne East Village Sleep Medicine in Des Moines, Iowa. These listings are maintained by MercyOne and WebMD, not by Complete Sleep:
Complete Sleep is independent and is not affiliated with or endorsed by MercyOne or WebMD.
Articles on Complete Sleep (30)
Insomnia: What It Is and What Actually Helps
Insomnia explained: how it is defined, why it becomes self-sustaining, why CBT-I is the first-line treatment, and when to see a doctor.
Jet Lag Explained: How to Recover Faster
Why crossing time zones scrambles your body clock, why flying east is harder, and a practical plan — light, timing, naps, melatonin — to recover in days.
Shift Work and Sleep: Coping With Night Shifts
Night and rotating shifts fight your body clock. A practical guide: anchor sleep, light, caffeine timing, naps, the drive home, and when to see a doctor.
Winter Darkness, Short Days, and Your Sleep
Why sleep and mood sag in northern winters, how daylight sets the body clock, what morning light and timing do about it, and when low mood needs a doctor.
Daylight Saving Time and Your Sleep
What the clock change does to your body clock, why spring forward is harder than fall back, what research shows about the days after, and a four-day plan.
How to Sleep in Hot Weather
Why your body has to cool down to fall asleep, what heat and humidity do to sleep, and evidence-based ways to sleep better in summer — bedroom, bedding, timing.
How Much Sleep Do I Need? A Guide by Age
Recommended sleep hours by age from the AASM and CDC tables, why individual needs vary, the signs of too little, and when to see a doctor.
Why Do I Wake Up at 3am? Causes and What Helps
Waking at 3am is common. Learn why the second half of the night is lighter, what stress, alcohol, light and sleep apnea add, and what actually helps.
Melatonin for Sleep: What It Does and Doesn’t Do
Melatonin is a timing signal, not a sedative. Where the evidence supports it, where it is weak, how much to take, when, and who should ask a doctor first.
Snoring: When It Matters and What Helps
Why adults snore, what makes it worse, the red flags that point to sleep apnea, when to see a doctor, and the measures that quiet simple snoring.
Napping: How to Nap Without Wrecking Your Night
Is napping good for you? The ideal nap length and timing, how a caffeine nap works, why to skip naps with insomnia, and when sleepiness is a red flag.
Restless Legs Syndrome Explained
Plain-language guide to restless legs syndrome: what it feels like, why it is often missed, links with iron and pregnancy, and when to see a doctor.
Exercise and Sleep: When to Work Out
Regular exercise improves sleep quality and helps you fall asleep faster. What the research says about evening workouts, timing and your body clock.
Are Sleep Trackers Accurate?
Sleep trackers estimate sleep from movement, heart rate and oxygen. Learn what they get right, where they fall short, and when a sleep study is needed.
Sleep Paralysis: Why It Happens, What Helps
Sleep paralysis is frightening but harmless. Learn what causes it, how common it is, how to end an episode, and when it may point to narcolepsy.
Caffeine and Sleep: How Late Is Too Late?
Caffeine lingers for hours. Learn the half-life, the six-hour study, hidden sources in mg, decaf facts and a two-week test to find your own cut-off.
Does Alcohol Help You Sleep? Why a Nightcap Backfires
Alcohol makes you fall asleep faster, then breaks up the second half of the night: less REM, more waking, worse snoring and apnea. What to do instead.
What to Eat Before Bed: Late-Night Eating and Sleep
Meal timing beats 'sleep foods': late meals and reflux, the two-to-three-hour rule, light snacks, and the thin evidence for tart cherry and magnesium.
Anxiety at Night: Why Worry Peaks at Bedtime
Why worry feels loudest in bed, how an anxious night differs from an anxiety disorder, and CBT-informed tools that calm the mind so sleep can come.
Sleep and Depression: How They Feed Each Other
Sleep problems and depression feed each other. Learn the typical patterns, why CBT-I helps mood, how antidepressants affect sleep and when to get help.
Screens Before Bed: What the Evidence Actually Says
Blue light is only part of the story. A calm look at what screens before bed really do to sleep, why night mode underdelivers, and a rule that works.
Why You Wake Up Tired After 8 Hours of Sleep
Slept a full night and still exhausted? Why sleep inertia, social jet lag, alcohol, sleep apnea and low iron cause morning tiredness, and what helps.
Sleep Quality vs. Time in Bed: Why Quality Wins
You can spend nine hours in bed and still wake up tired. What sleep quality means (with the 85% benchmark), why extra time in bed backfires, and what unrefreshing sleep can signal.
10 Lifestyle Changes That Help Sleep Apnea
Weight, side-sleeping, alcohol, smoking, nasal congestion and more — the lifestyle habits that support sleep apnea care, with the evidence behind each.
10 Ways to Manage Stress Before Bed
A racing mind at bedtime is common and manageable. Ten practical ways to lower arousal in the evening, what the evidence says about each, and how to tell stress from anxiety that needs care.
Sleep Hygiene Tips Everyone Should Know
Sleep hygiene explained: what it is, the eight habits that matter most with the evidence behind each, the common mistakes that undo them, and when habits are not enough.
How to Build a Healthy Bedtime Routine (Adults)
A practical guide to a bedtime routine for adults: why routines work, a 60-minute wind-down you can repeat on your worst day, what to do when you cannot sleep, and when a routine is not enough.
At-Home Sleep Apnea Tests Explained
How a home sleep apnea test works, what it measures, who it suits, who needs an in-lab study instead, and what results mean — explained without the sales pitch.
Sleep Apnea: Symptoms, Risks, and Treatments
A plain-language guide to sleep apnea: obstructive vs. central, signs to notice, health risks, how it is diagnosed, and treatment options.