Hmmm... have you injured your back dancing? Do you maintain a strong core & good posture? Very important. Also, people who sit at a desk all day often have a weak core as we are not naturally designed to be seated all day. We should be moving around! See a GP & he may refer you to a physio if required. It could be muscular or skeletal. Good luck.
Ps: make sure you have a good, supportive mattress & sleep on back or side, not front.
Try sleeping on your front for a bit with the feet on the edge.