I've had two and both times couldn't finish the stuff they make you drink - once I was sick with the flu and once had a huge ovarian mass squishing everything in my abdomen. But that was the only problem - it took me forever to drink the part that I could, and I had to wait ages for it to work so I could go get the scan. Both times were unexpected so I was panicking, freaking out and just having to sit there terrified. But the scan itself? Over in like ten minutes.
Basically, if you don't get yourself worked up over it, it'll be easy. Bring a book or something, though.