Sacrum n lower back pain doc said may be caused by a double loop cyst at s2 (racepinephrine). suggested surgery. why do some cysts cause symptoms but others don't?

Not sure what you : Mean by "double loop cyst." he may be referring to a benign incidental finding (usually noted on your lumbar spine mri), which are mostly asymptomatic called tarlov cysts, which are perineurial cysts. Only on very rare occasions could this be the cause of your symptoms. So go have a spine surgeon evaluate you and give you a better answer after a physical examination and review of your mri.

Nerve comprestion: Cyst can compress nerves and cause pain. They seldom just disappear. You should get a second opinion if you want.