This has happened to me twice.
I am on PD and use a cycler machine at night for 9 hours. Sometimes I'll have to get up and go to the bathroom. Not to be gross or anything but when i feel like I have to do a #2 and I push at all I immediately get sick to my stomach.
The first time I did actually get sick. The 2nd time i almost got sick. I think both times I was on a dwell cycle.
What in the heck is going on ?? Am I just too full?? If I stop trying to go then the feeling goes away. Weird.