The trekking season is upon us, and it would be wise to remind ourselves of the warning signs of altitude sickness. Consider acute mountain sickness (AMS) to be a red flag. As you trek at about 2,500 m or higher you may suffer from hangover symptoms, headache and nausea. But if you descend a few hundred meters, you may feel these symptoms subside. With AMS, it is likely that you will get better if you don't go any higher, or descend right away.
Peer pressure, an overriding ego, or wanting of their money's worth from the trek can make people with AMS go in denial of their weak condition. Dangerous complications ensue when they push themselves and try to ascend higher. Water collection in the brain (high altitude cerebral edema, HACE) or in the lungs (high altitude pulmonary edema, HAPE) occur, as water seeps out of the blood vessels in these organs due to lack of oxygen brought upon by the inability to acclimatise properly. Symptoms of HAPE and HACE thus mandate immediate descent (by foot, yak, horse, a porter's back, or a helicopter).
Preventive aspects of "Lekh Lagne" (altitude sickness in Nepali) include the practice of listening to one's body. The sea level rule of "when the going gets tough, the tough get going" clearly does not apply at high altitudes, and strong and silent 'John Wayne attitude' would be life-threatening indeed. So don't rush up the mountain. Drink adequate fluids (about 3 liters per day), do not sleep higher than 300 to 500 m from the previous night's altitude, take a rest day every third day of your trek, practice the "climb high sleep low" technique, and take 250mg of diamox (acetazolamide), if you don't have sulpha allergy, two times a day if necessary.