What this solves
Above ~3,500 m, your breathing reflex becomes unstable. Up to 40 % of trekkers develop periodic breathing — a crescendo-decrescendo pattern that wakes them up gasping. That is normal. But insomnia that does not include that pattern, or insomnia with a morning headache, can be early AMS. This tool keeps you from treating a warning sign as a quirk.
What happened last night?
How to read the result
Normal periodic breathing — Above 3,500 m, the low-oxygen drive over-shoots. You breathe fast for 10–20 s, blood CO₂ drops, breathing almost stops, CO₂ rises, breathing kicks in again. If the pattern is cyclical and you wake up gasping but feel fine by morning, this is just altitude, not AMS.
Concerning — hydrate / no caffeine after 14:00 — Restless or wakeful nights without the cyclical pattern are usually sleep hygiene, dehydration, or anxiety about the climb. Fixable.
Warning sign — descend — Wet breathing, morning headache with vomiting, or non-cyclical insomnia with AMS symptoms are no longer "bad sleep." Treat as AMS, score it, descend ≥ 500 m.
Limitations
FAQ
A: No. Periodic breathing is uncomfortable but not dangerous by itself. The worry is when you stop sleeping enough to develop AMS — at that point descend, do not push through.
A: Acetazolamide 125 mg twice daily reduces periodic breathing. Avoid standard sleeping pills at altitude — they depress ventilation and can worsen SpO₂ dips. If you need a sleep aid, ask a travel-clinic doctor about low-dose zolpidem, not benzodiazepines.
A: The "second-night effect" at altitude is real — your body is still adjusting to hypocapnia. By night 3 most people improve. If it doesn't, that's the signal.
A: Yes. Cold stress worsens periodic breathing and fragments sleep. A 0 °C comfort-rated bag at Luorong (4,080 m) is not a luxury.