system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Can someone explain why you sometimes break out in sweat before you have explosive diarrhea?

Asking for a friend.
gpt
It's due to a vasovagal response.  The Vagus nerve can be stimulated during a bowel movement when you strain.  Bearing down can cause the veins in the legs to dilate causing a sudden drop in blood pressure triggering your vagus nerve.  Severe attacks can cause fainting.  Unless you faint, vasovagal responses or attacks are benign and are fairly common.