The small Bowel follow through is literally what it says. You go to radiology and drink a yucky strawberry rendition of barium, probably about a quart. Then you wait around for maybe an hour, and the techs start taking upper abdominal x-rays. They literally "follow" the barium "through" your digestive process with a series of x-rays - first of the stomach, and as it flows through your small intestine. So they have a bunch of x-rays that mark the course of the barium until it goes to the large colon. They literally "follow" the barium "through" your small intestine.
When my disease first onset (in 2002), I had a partial obstruction and thickening and narrowing of the ilium. At its smallest point, my ilium had narrowed from 35 mm to 11mm. That is quite small. I was literally spewing puke any time I ate. At times I had diarrhea. I could not hold anything down. It took 8.5 hours for that barium to start moving into the small intestine do to thickening. Normally the follow-through usually is over in 2-3 hours.
Funny thing is they never gave me the dx back then, and I obviously had Crohn's, but I didn't know it. They found a more ominous problem - a tumor on my lung. So my gut became the lesser priority. They did put me on a liquid diet for 2.5 weeks, and that got the situation under control. I was so afraid to eat anything, that even after the liquid diet I ate like a bird because the memory of that upper gut pain was seared into my mind.
I gave my GI the reports from the narrowing ileum and partial obstruction in 2002 last month when I went in for a c-scope and EGD. He took one read and and told me the same thing from 2002 was happening to me in this July because I had the same symptoms, but milder. The irony was that after my procedures, my GI back-dated my diagnosis from 2 years ago to 2002. So technically, I was in complete remission from January 2003 until July 2009. News to me, until I read the reports a couple days later.
I've had 4 colonoscopies and two upper EGD's over the past three years since my disease became active again. You'll probably tolerate both procedures pretty well. They aren't harrowing or extremely painful or too uncomfortable. Bring something to read for the follow-through. These tests are pretty reliable and should shed some light on your condition or conditions.
Good luck, and don't obsess or worry. You should do fine. The barium will give you diarrhea for the rest of the day, and your poop will become white. That's probably the worst of it.