The Atlas and Axis vertebra are like the main switch at the fuse box. If they're off you're going to have trouble. So yes, get your upper neck checked out but also the pelvis/low back. With the situation you described you may have set up a "reflex" to hold it in. But it should clear itself out within a week.
It wouldn't hurt to get the spine checked out, both neck and lower back. A good chiropractor will check them both anyway. It's very seldom you have one without the other getting involved. But it apears to me that if you didn't have any trouble before and now you do get a good bowel mover and take that for a few days to normalize the parastalsis. Barefoots LBB or Schulzes Formula #1.
But yes, the upper cervical spine does have an effect on the musculature of the colon.