A Candid Field Report From 12,500 Feet: Your First 48 Hours at Altitude

You step off the plane in Cusco, La Paz, or Quito, and for about ninety minutes you feel suspiciously fine. Maybe a little winded on the stairs. Maybe a tiny flutter in your chest. You think: This is what everyone warns me about? Then dinner arrives, and so does the headache.

Altitude at 3,800 meters — roughly 12,500 feet — isn't a hangover, even if it feels like one. It's a predictable physiological event. Atmospheric pressure is lower, so each breath delivers less oxygen. At that elevation, the partial pressure of oxygen in your lungs is about 60 percent of what it is at sea level. Your body notices immediately, even if your brain takes a few hours to file the complaint.

This is a field report, not a medical lecture. But if you're a US traveler used to sea-level cities and weekend hikes at 6,000 feet, it helps to know what the next 48 hours actually look like.

Hour Zero to Six: The False Confidence

Most people land, check into their hotel, and do too much. They walk uphill to a viewpoint. They order a big lunch. They unpack and reorganize and text everyone back home about how great they feel.

That window is a trap. Your body is still running on borrowed oxygen and adrenaline. The first real symptom is usually breathlessness on stairs — not dramatic, just annoying. You'll pause mid-sentence to catch your breath. You'll feel a little lightheaded when you stand up fast.

This is the moment to do almost nothing. Drink water. Sit down. Eat something small and starchy. Resist the urge to prove you're acclimatizing faster than everyone else in the lobby.

Night One: The Sleep That Isn't

Altitude sleep is a strange animal. You're exhausted, you fall asleep, and then you wake up at 2 a.m. feeling like you forgot to breathe. You didn't — but your breathing pattern at altitude is different. You may experience periodic breathing, where your breath pauses for a few seconds and then restarts with a little gasp. It's normal. It's also terrible for sleep quality.

You might wake up with a dry mouth, a dull headache, and the vague sense that you've been camping in a wind tunnel. Your heart rate is higher than usual. If you have a pulse oximeter, the number may be in the high 80s. That's common at 3,800 meters. It's not automatically an emergency — but it's also not a number to obsess over at 3 a.m.

What helps: keep the room cool, prop your head up slightly, and don't drink alcohol. A sleeping pill is a bad idea unless your doctor has specifically cleared it; it can blunt the breathing response that altitude already disrupts. Over-the-counter pain relievers for a headache are fine for most people, but read the label and know your own health history.

Day Two: The Weird Appetite and the Small Wins

The second day is when the altitude hangover usually peaks. You may feel foggy, irritable, and oddly uninterested in food. Or you may feel ravenous for carbs and nothing else. Both are normal. Your appetite is being rewired by a body that's working harder at rest than it's used to.

Eat small meals. Soup, rice, potatoes, bread, fruit. Andean highlands are excellent at this kind of food — think sopa de quinua, boiled potatoes with a little cheese, toasted corn. Don't force a steak dinner. Don't skip meals entirely, either. Your body needs fuel to make the red blood cells it's already starting to produce.

Hydration matters, but chugging four liters of water won't fix altitude. Drink to thirst, plus a little more. Herbal teas are fine. Coca tea is a cultural staple and a mild stimulant; it's not a cure, but it's a pleasant ritual and it keeps you sipping. If you're taking acetazolamide or another prescription preventive, follow your doctor's instructions exactly — don't improvise dosing because you read something on a forum.

Night Two: The Turning Point (or Not)

For many people, the second night is slightly better. The headache eases. You sleep in longer stretches. You wake up hungry. That's a good sign, but it doesn't mean you're ready for a 4,200-meter pass. Acclimatization is a slope, not a switch.

For others, night two is worse. The headache sharpens, nausea arrives, and you start wondering if you should have stayed home. This is the moment to be honest with yourself. Mild altitude sickness — headache, fatigue, poor sleep, loss of appetite — is common and usually passes with rest. But if you develop vomiting, confusion, a cough that won't quit, or breathlessness at rest, that's not a personality test. That's a signal to descend and seek medical care.

When to Stop Being Tough

The macho approach to altitude is a bad hangover from older travel writing. You don't win anything by pushing through a worsening headache. High-altitude cerebral edema and high-altitude pulmonary edema are rare but real, and they can escalate quickly. The single best treatment is descent. If you're with a guide, tell them. If you're on your own, get to a lower elevation and a clinic.

A pulse oximeter can be useful, but it's not a diagnosis. Readings vary by device, circulation, and altitude. Your doctor can give you a personal threshold to watch for. Don't self-diagnose based on a single number.

The Habits That Actually Help

Arrive slowly if you can. Take the bus instead of the short flight, or build in a night at a mid-elevation town. Skip the big hike on day one. Eat carbs, sleep when you're tired, and don't schedule a sunrise tour that requires a 4 a.m. alarm. Alcohol and altitude don't mix well. Neither do dehydration and altitude. Andean highlands are dry, and you'll lose more water than you realize just breathing.

Most of all, give yourself permission to be boring for 48 hours. The mountains aren't going anywhere. The best acclimatization plan is the one that feels almost too cautious — until you're the person at breakfast on day three who actually wants to walk to the market.