Oxygen deprivation is a real thing - and this weekend I experienced it for the second time. Thankfully both instances were not while flying.

A couple years ago I participated in oxygen starved training with the Portable Reduced Oxygen Training Enclosure (PROTE). They lower the o2 in a controlled environment, and you focus on what symptoms creep up. Different people have different effects in different severities.

In my PROTE experience, the main thing I noticed was time dialation. As the O2 levels dropped and I completed math and logic puzzles, I felt I could still write and generally think well. However, the few minutes we were in the chamber felt much longer. This probably means that my reflexes, speech, and thoughts were much slower than I expected. I started deep breathing. Not gasping breaths, but slow controlled lung-filling breaths. My body's way of trying to compensate.

I am a low time private pilot in Dallas where the elevation is a bit over 500. The highest I've ever flown outside of commercial airliners is about 7k. So in the years since my PROTE experience, I haven't had the opportunity to need o2.
Until this weekend.

I took my family to Colorado. 7k elevation at the hotel. I'm already starting at my highest flight. Then we decided to hike to Mount Evans. The drive is on the highest paved road in the US. Second in the world. Many sections are very narrow and most of it is just a few feet from a steep dropoff that would result in at least a long conversation with the car rental insurance company - and more likely with my health or life insurance folks. I've been skydiving, been upsides down in planes, had a few questionable landings, and once almost bent a stearman that didn't have insurance.
I have never been more nervous than driving on that road. Never.

Like many pilots, I'm afraid of heights. At least, that's what I use to say. I've evolved that thinking to say I'm afraid of risk. Controlled properly, a plane won't fall apart. A parachute has a backup. A helicopter can autorotate. Statistically, I know these things are reasonably safe, have oversight on them, and I can predict the outcome of most possibilities.
But put me on a second story ledge or balcony and I got problems. I've come to realize I don't necessarily have a fear of heights, but a fear of lacking control and unknown/unmitigated risk.

After the long and slow drive, there was still about a quarter mile-100 foot climb to the top. Mount Evans is just over 14,000 feet. The temperature dropped about 20F from the bottom, so my son and I had the opportunity to have a snowball fight in July. (Mom wasn't too pleased when we teamed up against her) :) it was a beautiful day. Blue skies above. Being able to see so much with your feet on the ground is an amazing experience. Still though, I would look out into the valleys and imagine cutting through them in a jet, skimming treetops, avoiding power lines (google that L-39 incident), and looking up thousands of feet at the peeks blocking the sky.

At some point in the climb, I started to notice my breath get a little deeper. Nothing else. No other symptoms, but my mind went to that PROTE experience for the first time since I did it, so I was very focused on noticing changes. It wasn't until we had spent a couple hours up high and had started walking back down until I noticed other symptoms. Little bit of a headache, elevated heart rate, and I thought there was a slight hue of blue to my finger tips. Otherwise, I didn't have any cognitive symptoms. The trek down was uneventful - except for the continued anxiety of the height.

So... A great hike with the family, amazing views, and recognition of symptoms because of PROTE. It was another opportunity to feel these affects and be aware of how my body reacts in case I find myself up high in a more risky situation.
Knowledge and experience increase comfort, and mitigate risk.