The stretching of the discs or whatever also occurs here on earth. I saw a piece on it on one of those cheesy 20/20 or 60 minute type shows where they had people measure themselves on a wall before they went to sleep, and then had them measure themselves on the wall right after they woke up in the morning. The people were usually 1-2 inches taller in the morning because while you're sleeping (and therefore usually laying down) gravitity isn't vertically compressing your spine, which somehow allows the discs to expand. Of course, during the normal course of the day we get compressed back down to our normal heights. Kind of interesting.
