I've been known to go from C to D pretty quickly. I have a natural tendency to be a little C anyways, but when the gall bladder went bad, suddenly I would have a somewhat constipated poop followed less than 30 minuted later by bile diarrhea. Even now I can have a normal poop or even one that's slightly constipated and a little while later have big, very soft poop.
Here's my theory on it: So you eat over the course of today and the food goes through your digestive tract and winds up down low, ready for there to be enough of it to trigger a release. Maybe you just don't get triggered tomorrow morning, or maybe your intestines just decided to absorb too much water or you took an anti-diarrheal pill or ate something constipating like dehydrated banana chips--whatever. So when you do finally poop tomorrow evening or even the day after, that original stool is kind of hard. But what about all the other foods you have been eating in the meantime? They've been going through too. And maybe you got stressed or released too much bile or your intestines refused to absorb water--whatever--and that stool never gets really formed. So you do the first one and the second one takes an hour or two to move into place at the end and when it comes out, it's all watery. What I am eating now for lunch will cause that related stool to be one way, based on the condition of my intestines and what I eat. What I eat for supper will have a different set of variables and the stool related to it can be different from the one caused by what I'm eating now. Just because they all come out of the same place doesn't mean that each part doesn't have the potential to be unique. If that makes any sense. At least that's my theory.