Sleep apnea 101 — what it is, what it does, what to do.

If you're reading this because you suspect you (or your partner, or your parent) might have sleep apnea — start here. I'll write the version of this explainer I wish someone had given me before I spent two years thinking I was just a heavy sleeper.

I'm not a doctor. I built a sleep app because nothing else helped me figure out my own situation. What follows is what I learned along the way, plain enough to use as a starting point. The actual diagnosis still has to come from a sleep specialist — that's not a hedge, that's just how this works.

The simple version

Sleep apnea is when your breathing repeatedly stops or significantly slows during sleep. Each event lasts at least 10 seconds. They happen because your airway either collapses (the most common kind, "obstructive") or because your brain briefly stops sending the signal to breathe (the rarer kind, "central").

Most adults have a few of these events a night even when "fine." The clinical question isn't "are they happening" — it's "how often per hour, and how much oxygen are you losing each time."

The metric you'll keep hearing about: AHI

AHI = Apnea-Hypopnea Index. It's the number of breathing events per hour of sleep. The clinical thresholds:

SomniSense reports a metric called BRI (Breathing Irregularity Index) which is the same per-hour event-rate scale. The thresholds align. More on the difference between BRI and AHI here.

What it actually does to you

Each apnea or hypopnea event drops your blood oxygen briefly. Your body responds with a small adrenaline spike, your nervous system arouses you (briefly, usually below conscious memory), you breathe again, and the cycle repeats.

The visible consequences:

• Daytime fatigue. You slept 8 hours but your body got a fragmented version of those 8 hours. Coffee partially compensates.
• Morning headaches. CO₂ retention overnight + cerebral vasodilation. Bilateral, pressing, fades within an hour or two.
• Brain fog and reduced focus. REM and deep sleep get cut into pieces. Memory consolidation suffers.
• Mood changes. Irritability, low patience, sometimes mild depression-like symptoms. Often mistaken for "just being tired."
• Partner-observable signs. Loud snoring, gasping arousals, witnessed pauses.

The less visible consequences over years:

• Hypertension that doesn't respond well to medication. The constant nervous system arousals raise blood pressure baseline.
• Cardiovascular risk. Untreated moderate-to-severe OSA correlates with heart disease, stroke, and arrhythmia over decades.
• Metabolic effects. Insulin resistance and weight gain feed back into worsening apnea.

That last list is the reason this matters more than "you're tired in the morning." The morning fatigue is the symptom you'll notice. The cardiovascular impact is what makes treating it worth real effort.

How it gets diagnosed

The standard pathway in the US looks like:

1. You notice symptoms or your partner does. Or a wearable flags something. Or your dentist sees the airway and asks. Many entry points.
2. You see your primary care doctor. They ask about symptoms, look at your airway, check your blood pressure. If sleep apnea is a likely fit, they refer you to a sleep specialist.
3. Sleep specialist consult. They take a more detailed history. If a study is warranted, they order one of two things:
• Home sleep apnea test (HSAT) — a small device with a chest band, finger sensor, and nasal cannula. You sleep 1-3 nights at home wearing it. Cheaper, more convenient, sufficient for most uncomplicated OSA cases.
• In-lab polysomnography (PSG) — overnight in a sleep lab with full sensor setup. The gold standard. Used for complex cases or when an HSAT was inconclusive.
4. Diagnosis. AHI from the study determines severity and treatment options.
5. Treatment. Depending on severity and your specifics: lifestyle changes, positional therapy, CPAP, oral appliance, sometimes surgical options.

From "I noticed something" to "treatment plan" is typically 3-6 months in the US system. Faster if you push and have insurance. Longer if your area has a backlog of sleep specialists.

Where SomniSense fits in this pathway

SomniSense doesn't diagnose anything. We're a wellness monitoring app, not a medical device. What we can do is help you figure out — quickly and cheaply — whether the formal pathway is worth starting.

Concretely:

• Step 0 — you're not sure if you have a problem. Run SomniSense for a week or two. The data will give you a strong hint about whether your BRI is in normal, mild, moderate, or severe range. If it's moderate or severe, the answer is yes, see a specialist. If it's normal, the answer is probably "look at other causes of your fatigue."
• While in the specialist queue. SomniSense data over 30 days gives the specialist much more context than a single intake conversation can produce.
• While in treatment. SomniSense can show whether your CPAP, pillow, side-sleep training, or weight loss is moving the numbers — over weeks, not just on a single follow-up visit.

What SomniSense can't do: replace the formal diagnosis. The HSAT or PSG is what your insurance and your treatment plan are based on. We're a complement to that pathway, not a substitute.

The risk factors most people don't know about

• Neck circumference over 17 inches (men) / 15 inches (women) is a stronger predictor than overall BMI.
• Recessed jaw or small airway anatomy. Some people are anatomically predisposed regardless of weight.
• Family history of sleep apnea. Real genetic component.
• Post-menopause in women. Risk roughly doubles after menopause; women are still systematically underdiagnosed because of historical research bias toward men.
• Heavy alcohol use. See our wine experiment articles for the data.
• Certain medications. Sedatives, opioids, some sleep aids.
• Hypothyroidism. Underdiagnosed, often co-occurs.

If two or more of those apply to you, the threshold for getting checked should be lower.