Why am I stiff when I get out of bed?
Although it could be a more serious condition, most of the time it is caused by microtrauma and improper spinal recovery. Imagine a cut on a knuckle that you just keep ripping open and when it heals you let a wool blanket stick to it. When you wake up, you rip it off. Yeah, not fun but most of us do this every day. We work at a desk or standing in a limited area with our spines in poor positions. When we sleep we tend to duplicate the same position that we work in. This allows our spine to heal incorrectly. Sleeping is very important to maintaining the health of our spine.
Sleeping is also the only time that we gain height! It is true that when we sleep we rehydrate our discs and it actually makes us taller. It is a very small but important amount. Our discs are made of soft tissue or mostly water. When we sleep there is no compression on the discs so they are allowed to fill. The way we sleep can allow more fluid to expand on the back side of the disc which will put us at higher risk for herniation. This is why it is important to sleep on a firmer mattress if you are a back sleeper or straighter, on your side with a pillow that extends between your knees to your ankles.
The stiffness you feel is because your discs expanded but your muscles did not get more flexible. This is why it is important to be very careful in the morning to not do things that will put excess stress on your back. This stretching or stiffness can also be the nerves in the discs as well. Our brains do not understand what a disc feels like so it relates it to something we understand. Usually achy, stiff, sore, and sometimes shooting pains.