Don’t panic! I wasn’t flying at the time. It was part of some training to experience the effects of hypoxia (lack of oxygen to the brain). Ideally you would go into a decompression chamber for the most authentic experience but this involved wearing a mask that delivered a gas mix that simulated flying at various altitudes. At the same time I wore a device that measured my heart rate and blood o2 levels and performed a number of tasks to demonstrate the mental effects.
I think the most interesting/worrying thing to come out of it is that I, personally, didn’t feel much different from normal. If I was to become hypoxic in flight for real I think I’d have no idea. I did experience certain symptoms but I could only identify them in retrospect and wasn’t aware of them at the time. Also many of them were very subtle and would be drowned out by normal environmental factors.
The most obvious symptom was that I couldn’t hear much. The background noise faded away. However I was only aware of this when the noise came rushing back after I received some O2 for a while. Other than that I had a brief very mild headache and difficulty concentrating. I got a little flushed and sweaty but that is a normal symptom of mental concentration for me so I’m not certain it was a valid hypoxia reaction or just a reaction to being put in a small room and asked to perform various tasks for seven minutes.
One of the tasks was to remember the position of a playing card in a 2x2 grid of cards. Initially I thought that I just have a crap memory but thinking back on it, I had no trouble the first time when I had normal o2 levels, it was only later that I found it difficult. It was probably the most severe mental symptom as it presented almost immediately and was bad enough that I couldn’t even remember if the card being shown to me was on the previous grid at all. I distinctly remember looking at a 2 of diamonds and thinking that they’d done something to the font of the upside down 2 and also thinking that I remember there being a 2 of diamonds in the top left corner of the grid but I was certain that it had many more than just 2 diamonds, I.e., it had the numeral 2 on the top and bottom but had many more than just 2 diamond symbols.
My heart rate started at around 80 and gradually climbed to 110-120 through most of it, then there was a rapid drop to the low 60s at which point the instructor aborted the test as a precaution. Meanwhile my blood O2 levels started at around 98% and stayed there for a while before gradually dropping. At the point the test was aborted my O2 was about 50% and it continued to fall to the low 40s after being given recovery O2. This is known as the oxygen paradox. It takes some time for the O2 to take effect and you initially feel worse before you get better.
The whole thing was captured on video and I have a DVD that I can watch when I get home.
All in all a very interesting experience.