Even though the doc thinks it's all in my head

he's gone an ordered a CT scan. I have to drink an "oral contrast" beforehand. I'm picking it up at the imaging center Saturday for my Wed. CT scan. I'm assuming it's barium.
So, how much am I gonna drink and is it nasty? I'm assuming I'll drink a lot and yep, it'll be gross. Just curious what I'm in for though, and would love to know how bad it is! Any side effects? Nausea, diarrhea?
I'm so sick of tests.