As you move around during the day, gravity puts a lot of pressure on your back. It’s up to the spine’s discs to protect your vertebrae from this compression. When they lose water, there is more wear and tear on the vertebrae as space shrinks between them. The outer layer of these discs can become damaged, causing bulging or herniated discs that can press into your sciatic nerve. This is what can cause radiating pain down your leg, according to Narayana Health.
These discs tend to lose their hydration throughout the day. Because you’re mostly upright during the day and continually compressing the discs, it’s difficult for your body to rehydrate the discs. In fact, you might notice you’re up to half an inch shorter by the day’s end because there’s less space between the discs due to reduced hydration, according to Arrowhead Clinic. At night, while you’re asleep, your body works to rehydrate those discs, restoring your height when you wake up.