Several factors can make back pain feel more prominent at night, and most of them are about attention and position rather than the underlying issue actually worsening.
Fewer distractions
During the day, activity and mental engagement naturally compete for attention with physical sensations — lying still at night removes those distractions, which can make ordinary background discomfort feel more noticeable.
Sleep position matters
Certain sleep positions place more strain on the lower back than others — stomach sleeping in particular tends to increase lumbar arch and strain, while side-sleeping with a pillow between the knees is commonly recommended as gentler on the lower back.
Mattress and support
An unsupportive mattress or one that's aged past its useful support life can contribute to nighttime discomfort independent of any underlying back condition.
Does lying flat make lower back pain worse?
It depends on the person and cause — some find flat lying uncomfortable and prefer a slight knee bend (a pillow under the knees when on the back), which reduces the natural arch of the lower spine.