Sleep apnea is a condition that causes you to stop breathing while you’re sleeping. The word “apnea” comes from the Greek word for “breathless.” Sleep apnea happens because you stop breathing in your sleep. This happens either because of blockage of your airway (obstructive sleep apnea) or because your brain doesn’t correctly control your breathing (central apnea).
The resulting lack of oxygen activates a survival reflex that wakes you up just enough to resume breathing. While that reflex keeps you alive, it also interrupts your sleep cycle. That prevents restful sleep and can have other effects, including putting stress on your heart that can have potentially deadly consequences.
Sleep apnea can happen to anyone, ranging from infants and children to older adults. Obstructive sleep apnea is more common in certain circumstances and groups of people:
Before age 50, it’s more common in men and people assigned male at birth (AMAB). After age 50, it affects women and people assigned female at birth (AFAB) at the same rate
People are more likely to develop it as they get older
Having excess weight or obesity strongly increases the risk of developing it
It’s more common in people who are Black, Hispanic or of Asian descent.
Central sleep apnea is most common in certain groups of people:
People who take opioid pain medications
Adults over 60 years old
People with heart conditions such as atrial fibrillation or congestive heart failure
For some people using CPAP or who have obstructive sleep apnea, this can trigger the development of central events knowns as treatment-emergent central sleep apnea
When people live at high altitudes, this can cause central apneas to occur.
Sleep apnea is uncommon but widespread. Experts estimate it affects about 5% to 10% of people worldwide.
To understand how sleep apnea works, it helps to know a little bit about the human sleep cycle. Sleep happens in multiple stages:
Stage 1: Light sleep. This is a short stage that begins right after you fall asleep. It accounts for about 5% of your total sleep time.
Stage 2: Deeper sleep. This stage is deeper and makes up about 45% to 50% of all the time you spend sleeping (this number goes up as you get older)
Stage 3: Slow wave sleep. This is the deepest sleep stage, making up about 25% of the time you spend sleeping (this number goes down with age). It’s very hard to wake someone up in stage 3 sleep, and waking up directly from it usually causes “sleep inertia,” a state of “mental fog” and slowed thinking. Parasomnias like sleepwalking and sleeptalking happen in this stage.
REM sleep: REM stands for “rapid eye movement.” This stage is when you dream. When a person is in REM sleep, you can see their eyes moving beneath their eyelids.
When you fall asleep, you typically enter Stage 1, and then move into and cycle between Stages 2 and 3. After cycling between those stages, you’ll ultimately go into REM sleep and start dreaming. After the first REM cycle, you start a new cycle and go back into Stage 1 or 2. One cycle normally takes about 90 to 110 minutes before another begins. Most people go through four or five cycles per night (assuming they get a full eight hours of sleep).