Advice on CT

Hi I wonder if anyone could tell me their experiences with having a CT colonograph please. I have gastrographin to take for it. But I am hoping I won't experience severe pain during procedure. 
I have had results this week of qfit>400. Been loosing weight, not much of appetite, diarrohea, urge to go and then not able to go, passing blood dark and fresh colour, abdo pains. It's good I Quickly got urgent sigmoidoscopy what they could see looks ok but couldn't go further to do a colonoscopy due to the severe pain I had and blood pressure dropped very low. 
so now I am now for urgent CT this week!