The tube for the 24 pH probe isn't too bad. It's pretty thin. You can feel it only when you swallow but I would say it's mildly uncomfortable, not horribly so. I do find as the day goes on, you get more used to it. I had the manometry test done earlier today, prior to the 24 probe. I found that one much more uncomfortable. The tube is much thicker. That test is supposed to measure how the muscles in your esophagus work, and how your LES valves are working. It also aids in the proper placement of the 24 pH probe. The manometry only took about 15 minutes, so it was bearable. I wouldn't have wanted to be sent home with that tube though.
I was lucky in that being off the meds didn't make my symptoms worse so that part was easy for me. (Guess mabye I'm not on the right meds or not being treated for the right condition!) I hope you do ok, being off your meds before your test. Did your doctor talk to you about wearning yourself off, instead of stopping all at once? I would think that might make things easier.
Good luck!