Tooth pain when lying down. The pain goes away within a minute of standing up. Any ideas?

I have a dentist appointment next week but looking for opinions. I had a root canal performed a few months ago, all went well and X-ray looks clear- BUT... When I lay down that tooth hurts, as well as the one next to it. It does not throb in pain, it only bothers me when I touch it with my finger or tongue.