water as we lie down at night (taking the weight of gravity off the spine), and during the day when we are in an upright environment, the discs slowly lose water. Consequently, any minor disc issue/injury tends to be amplified early in the morning when the disc is more plump or full of water.
Additionally, discs are more prone to injury early in the morning. In other words, you can prevent low back injuries (and treat current low back issues) by avoiding bending forward the first 1-2 hours after waking up.
Snook SH, Webster BS, McGorry RW, Fogleman MT, McCann KB. The reduction of chronic nonspecific low back pain through the control of early morning lumbar flexion. A randomized controlled trial. Spine (Phila Pa 1976). 1998