A couple of days ago I went to bed at 8 a.m., then 10 a.m. yesterday, and probably noon today. I wake up at dinner time. It's just like having jet lag.
Although I avidly try to avoid moving to a later and later bedtime, my body's clock is ultimately in charge. If I have pain that disallows sleep, I've immediately lost any hope of a bedtime that makes sense. With pain, my nurtured bedtime proves to be quite unsupported in comparison to what my body's clock has known as "days".
As with many symptoms, it has taken me a long time to realize my lengthening sleeping cycle (noticed for 15 years now) was largely due to brain/pituitary functions. It often seemed there were other reasons...