AMS Altitude Sickness Basics: Headache, Nausea, and Insomnia Are Your Body's Warning Signs

Introduction

Taiwan has more than 200 peaks above 3,000 meters, from Yushan (Jade Mountain) and Xueshan (Snow Mountain) to the Hehuan mountain range, attracting over a million visits each year. However, at elevations above 2,500 meters, approximately 25–40% of people will experience Acute Mountain Sickness (AMS). AMS is not a matter of “poor physical fitness”—it is a signal that the body has not yet completed its physiological adaptation to a low-oxygen environment. This article uses the Wilderness Medical Society (WMS) framework and the Lake Louise Acute Mountain Sickness Score (LLS 2018 revision) to help mountaineers recognize early warning signs.

Why AMS Happens

The higher the altitude, the lower the atmospheric pressure, and the partial pressure of oxygen (PiO₂) drops, leading to a decrease in arterial oxygen saturation (SpO₂). The body initiates compensatory responses: heart rate increases, breathing becomes deeper and faster, and cerebral blood flow increases. However, if increased cerebral blood flow is accompanied by mild leakage of the blood-brain barrier, it can cause brain volume expansion, resulting in headache and nausea.

Common triggering factors:

• Ascending too quickly (gaining >500 m per day above 3,000 m)
• Dehydration or sleep deprivation
• Individual susceptibility (prior history of AMS increases risk ×3)
• Concurrently exercising at excessively high intensity

The Lake Louise Scoring System

The 2018 revision scores 4 symptoms, each rated 0–3:

A total score of ≥3 points with headache is sufficient to diagnose AMS. 3–5 points is mild, 6–9 points is moderate, and 10–12 points is severe (HACE must be suspected).

Insomnia: The Most Underestimated Early Sign

High-altitude sleep is often accompanied by periodic breathing (Cheyne-Stokes respiration): breathing pauses intermittently for 10–20 seconds followed by gasping, along with frequent awakenings. Mountaineers often mistake this for “just not sleeping well in a different bed,” but insomnia combined with headache is already considered a strong indicator of AMS in the LLS.

Practical Recommendations

• Spend the night before at 2,000 m: for example, before staying at Hehuan Mountain Lodge (3,150 m), spend the previous night in Cingjing (1,750 m).
• 24-hour golden observation window: symptoms are most pronounced 6–12 hours after arrival; if not improved after 48 hours, descend.
• Give NSAIDs first for headache: Ibuprofen 400 mg every 6 hours can relieve high-altitude headache.
• Avoid alcohol and sleeping pills: both suppress respiratory drive and worsen nighttime hypoxia.
• Note for cyclists riding Wuling: if you ride from Cingjing all the way up to Wuling (3,275 m) and descend the same day, delayed-onset AMS can still strike the next day after you return home.

Conclusion

AMS is the body’s benevolent alarm, not a source of shame. By learning to self-assess with the Lake Louise score and understanding the physiological mechanisms behind insomnia and headache, mountaineers in Taiwan can go farther and safer on Yushan, Xueshan, and Hehuan. In the next article, we will further discuss the critical warning signs of AMS progressing into HACE (high-altitude cerebral edema).

Related Reading

• Altitude Sickness and Cycling: High-Altitude Adaptation You Should Know Before Riding Wuling
• High-Altitude Risk in Children: Overnight Stays Above 3,000 Meters Not Recommended for Under 8
• Staged Ascent to Prevent AMS: Climb No More Than 500 Meters Per Day
• HACE High-Altitude Cerebral Edema: The Fatal Warning Sign That Deteriorates Within 12 Hours