I have had this a couple of times and I will tell you why it happens:
It has to do with your intestines being in distress, like one time it was because I had sudden diarrhea based on something I ate. LOL - this was at a mall - I was used to eating nearly nothing (a constant dieter) and my mom took me out to lunch so I indulged in a quiche AND cheesecake. If you can even imagine the fat content of that meal - well, I remember RUNNING up the escalator stairs to find the department store bathroom. Once inside the stall I felt so distressed and HOT that I stripped off my shirt (TMI, I know, but the point is - I was overheated suddenly and in great distress.) Better a few minutes later.
The other time was less funny but I was taking meds that slow the bowels down (opposite problem as diarrhea.) Actually I had to stop the meds because I knew that people can't go a week without moving bowels - it just can't be healthy. In my mind I'm sure I had some sort of blockage going on but without the meds in my system, the intestines finally took over but it was kind of traumatic. When I finally did have to go I had what others described - shaking feeling, rather distressed, and again, hot enough to strip off clothes. I don't take that med anymore. It was a tricyclic antidepressant and doctors never believed me when I said it locked up my bowels - and I mean into lockdown mode. They told me to just try bran, prune juice, etc. - nope, no help. I had to just stop taking the med periodically and eventually I stopped taking it altogether. Those meds are known for causing "ileus" and I have been "pooh-poohed" (pun intended) for saying they can cause severe bowel dysfunction but I know it's true.
So, in summary, I think this is caused by a distressed intestinal system (any connection to cancer would be rare since there are a million other reasons for bowels/intestines to become distressed, like either diarrhea or constipation.) I would bet on constipation being the culprit if you have that. I once saw my child become very distressed due to constipation; we almost took her to the E.R.
I think it is, technically, as others have said, a nervous system phenomena where whole-body effects arise from the intestines (an important part of your body) having a temporary crisis.