I don't know whether this might be the reason or not, but I've heard that, sometimes, people can appear taller in the morning than later in the day, because of something to do with the spine. I think it's supposed to be that the spinal discs are compressed during the course of the day, when the person is up and about, but when they are sleeping the pressure is relieved.
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Blackbird singing in the dead of night, take these broken wings and learn to fly...