I am sure that at least half of my engineer friends/family will correct this definition, as this is based on fuzzy descriptions from about 15 years ago, but basically, a pressure vessel is a vessel that can sustain pressure from the outside, like a submarine (or can keep pressure inside, like a pressure cooker). So, as I contemplated pressure vessels, and how I was hurtling through the atmosphere in one, I then started thinking about the fact that all pressure vessels have a limit to the amount of pressure they can sustain (which is why the bombs in Boston last April were particularly devastating). No, I wasn't getting morbid in my sleeplessness... Somehow explaining your thinking seems to take longer than the actual thoughts!
Anyway, I then realized that my body is basically a pressure vessel. There have been a few CSI episodes where a body has "popped" because of the buildup of gas from the decomposition process. And so, that thought led to thinking that, as humans, we need pressure vessels like planes or submarines because we don't do particularly well when the pressure is too high or too low... We are at equilibrium with our surroundings because our internal pressure pushes back on the external pressures.
Which brings me to my point--emotionally we are similar to a pressure vessel, too. If we live with too little or too much stress for too long, we don't do very well. With too little stress, we (or at least I) tend to get bored and restless. With too much stress, we get physically sick, irritable, and we often start living our life perpetually defensive. Life becomes something to retreat from rather than something to embrace with a breath stealing bear hug. Just like a pressure vessel, we either expand, sometimes explosively, or we collapse on ourselves.
So far, in spite of the fact that I have maybe had about 4 hours of sleep in the last 24, I am leaning toward the "just right" category of stress. This pilgrimage is a way to reset and evaluate, and yet, we should all reset and evaluate from time to time. Where is your pressure gauge at?