Final answer:
Lower back pain when lying down can be caused by muscle strain, herniated discs, or other spinal problems, often exacerbated by incorrect lifting or the physical changes during pregnancy. Disc herniation particularly affects the lower lumbar region and can lead to sciatica or, if in the cervical spine, to neck and limb pain.
Step-by-step explanation:
Lower back pain when laying down can be due to various reasons including muscle strain, herniated discs, or other spinal issues. For instance, pregnant women often suffer from back strain late in their pregnancy due to the added weight and shift in their center of gravity, which places extra stress on the back muscles and spine. Additionally, lifting objects incorrectly can create abnormally large forces in the back muscles and spine. This action can cause muscle strain and even damage to discs and vertebrae. Furthermore, a herniated disc can occur when the nucleus pulposus, the gel-like center of an intervertebral disc, protrudes through a weakened anulus fibrosus due to the pressure exerted on the disc when bending forward and lifting heavy objects. This can lead to compression of a spinal nerve and result in pain or muscle weakness.
Disc herniation often affects the L4/L5 or L5/S1 intervertebral discs, which can lead to sciatica – a pain that radiates from the lower back down the thigh and into the leg. Similarly, injuries to the intervertebral discs in the cervical spine can cause neck, shoulder, and upper limb pain. It's important to note that without the sensation of pain, a person might not realize the extent of the injury and could potentially worsen the condition by not resting or seeking appropriate treatment.