I got one before because my doctor thought I maybe had cancer. Turned out I didn't. Still glad I got it.
Basically the prep is the WORST part. I had to drink from two large pitchers of gatorade mixed with an entire bottle of Miralax. Yes, an entire bottle. I had to drink from the pitchers every 15 minutes until all the liquid was gone. You will shit like never before. You will be starving after you stop shitting your brains out, but unable to eat until after the procedure the next day. It SUCKS.
The procedure itself is painless. For me all I remember was seeing a nurse beforehand for a brief explanation of what will happen and then she got my vitals. Then I went to the room for the procedure, I laid down, they injected propofol into my body. I closed my eyes. I then opened them as I was growing impatient that I had not passed out yet, but when I did, IT WAS ALREADY OVER. Amazing!
You'll toss and turn in your bed and fart a bunch of times, and they'll go over your results. If it's nothing serious you'll get up and go home. It's that simple.
Hopefully your experience will be just as painless.