The most likely possibility here is that you are having something known as a vasovagal reaction. The vagal nerve is one of the most important nerves in the body, whose job is to regulate basic body functions, like blood pressure, heart rate, etc. In some people, a strong internal stimulus, such as a bowel movement and the intestinal contractions leading up to a bowel movement, can sometimes stimulate the vagal nerve, triggering all sorts of symptoms, like flushing, nausea, dizziness
, racing heart and, even, passing out. This set of unwanted symptoms is called a "vasovagal reaction."
I would recommend that you go to see your primary care doctor
about this issue. A vasovagal reaction is not in and of itself usually dangerous, especially if it is not happening frequently and if it does not lead to passing out or injury
. However, it is important for you to have a complete physical check up to make sure that these symptoms you are experiencing are not related to another, more serious medical problem. For instance, your doctor can check for any evidence of a heart problem and rule that out.
Make an appointment to see your doctor at your earliest possible convenience!