Either we adjust or we are self selected in the first place. Maybe both.<p>Taking many short flights for work practically forced me to learn to sleep sitting up even during the day if I was not fully rested. Many of my colleagues and frequently flying friends can do it too. But some people seem unable to do it. I found that once I understood I could do it, there was no further practice needed. Like riding a bicycle that half your friends always fall off.<p>In the past year I have slept in approximately 200 different beds. About once a month I do wake up in the middle of the night with the feeling that something is very wrong. Sometimes I don&#x27;t understand why there is no wall next to the bed, or why there is a window there. This feeling is acutely unpleasant, even alarming. But it goes away and I go back to sleep. It doesn&#x27;t seem to drag my sleep quality down.