Long sufferer of IBS but the last three days on and off wind and diarrhoea and in the last 12 hours non stop diarrhoea what's happening?

Viral infection? Acute illnesses such as a viral gastroenteritis, or food poisoning can often exacerbate otherwise stable IBS. Did you travel anywhere recently? Has any one else become ill? It seems like you know your IBS symptoms well, and what is happening now is clearly out of the norm for you. If there is blood in the stools, get checked ASAP. If not, viral gastroenteritis usually gets better in 1-2 days.