I learned about atonic colon a few years back when I was working for an Gi specialist. When being tested for a possible atonic colon, the patient swallows a capsule with radiographic rings - and abdominal x-rays are taken at certain intervals to see how long it takes for the radiographic rings to pass through the small and large intestine. Anything beyond 3 days is considered abnormal. My surgeon told me that there are many patients, who complain of severe constipation and end up being dagnosed with atonic colon - and have had their large intestine removed because of it. (They usually don't have any pain with bms either. Their main compliant is bloating.)
A surgeon would probably be more concerned with week bms - than a regular MD. A GI doc would probably be more concerned about it as well. AT least mine was. Because of my history with obstructions, my doctors don't want me to go any longer than 3 days between bms. If you ever obstruct, it will become more of a concern as well.