I've had a couple of colonoscopies without sedation and they were no big deal. In one there was some polyp removal, which I frankly dreaded, but, in truth, I didn't feel a thing and it was over before I realized it had started.
The prep for either procedure is pretty much the same… fasting, powerful laxatives, a lot of Miralax and hours of pooing soup … so there's really no difference.
As to a barium enema, there are three things that come to mind:
The embarrassment factor- It is a lot more embarrassing to have the barium nozzle put up you butt and inflated than be given 3000ml of thick heavy solution and then see the bag lowered, you poo it out back into the bag, then be refilled, or better inflated, with air, while the radiologist and nurse are doing it to you. Many people don't much like getting an enema with an audience of strangers.
The pain factor with a colonoscopy, the predominant feeling is of something big in your anus. It's not huge, but you can definitely feel it. Also, when the ‘scope' goes around the corners in you bowel it can be a bit ouchie. A good doctor will have the nurse press on the correct spot on you tummy and the ouchieness is brief and mild.
With a barium enema there is a lot of solution to go in and it can get crampy. Re-positioning on the table can help, but the volume is needed to see all the colon. When enough solution is in you and the bag is lowered, the relief is wonderful… until the air starts, when you feel like the Snoopy balloon at the Macy’s parade.
After either exam you fart a lot, but those after the barium can be wet and messy. There's no aftercare after a colonoscopy, but most people get a dose of laxative … sometimes mild, sometimes not … after a barium enema to clear out any residual barium.
The only other difference I can remember is the colonoscopy table is a lot less uncomfortable than for the barium enema.