is your dick at the bottom of your foot or something?
the cartilage in the spine tends to expand after a period of lying down (or weightlessness, like in space). it also tends to compress after sitting / walking around for a few hours. so people are almost always taller in the morning and shorter at the end of the day.
it's also the same for aging-- your cartilage gets worn down over time, causing you to lose height as you age.