I too would call your doctor and tell him what you've told us. That would be the safest way to proceed, and I'm sure his reply would put your mind at ease much more than anything we tell you here.
I had major bowel surgery a few years ago and I had a bowel obstruction afterwards. Since then I have had to have regular colonoscopies and I need to clean out before the surgery, just like you do.
Because I live in a different country, the preparations have different names to those in your country, but the one I take sounds similar to your's.
If your doctor says to go ahead and take the prep as ordered, do so very carefully. If you vomit, or if you had not had to visit the bathroom within 3-4 hours of commencing the prep, I would stop and contact your doctor before proceeding.
Good luck with the procedure. I hope you get a clean bill of health.
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