A few years back my kids had the norwalk virus and i remember it suddenly coming on. One minute they were playing and then it was like they made a retching sound and next it happened - out of nowhere. I got it next and i remember waking up in the early hours and i thought i'd sit and read a newspaper, like i generally do when i wake up. Next thing i am making that horrible noise and i get to the toilet in time. I only v* once. Didn't like it, but it happened. It came from nowhere. I couldn't believe how quick it came on. Other family members had it and they were the same - one minute fine, the next v*