I was misdiagnosed as having IBS a couple of years ago, and became addicted to oxycontin, because the pain was no severe I couldn't go to work without it.
At one point I had to have a colonoscopy, and I had to stop taking oxycontin 48 hours before the procedure, the withdrawl was hell.
I remember being scatter brained, unable to focus on anything for more than a few seconds, I was sweating and shivering, and it felt like my bones were on fire. The withdrawl caused a deep pain, especially in my joints, ankles and knees were the worst. It was a strange pain I had never felt before, like fire and electric. Even my teeth hurt.
It took 24 hours or so to get past the worst of it, and I have been VERY lucky to get another diagnosis and some medication that helps. I will never take oxycontin again, but sometimes, you just cant help it.