About Once A Year, For The Past 6 To 8

about once a year, for the past 6 to 8 years....I've experienced severe nausea during what seemed to be a normal bowel movement.....the movement continues....I break out into a cold sweat in my upper body....bowel continues to empty.....then the nausea passes and I'm completely fine. Any idea what is causing this as I never see it coming and can't identify any particular food that may be causing this.