That was my experience, when I had abdominal surgery in Mountain View, CA, in '96.
I was given morphine for the first four days, intraveinously. I self-medicated as little as I could stand, to try and keep my vision from blurring so much. I was told that I never came close to the maximum allowed dose in an 8-hour period.
When I got there, the nurse told me that she was going to be coming off her morphine. I was happy. About 15 minutes later, I was getting concerned because she was very sluggish and non-responsive. Finally, she passed out. I demanded that the nurse come down immediately, but it was nearly an hour and a half. The nurse had put her on what is known as a "Bolos Dose" which is a post-load dose that's about 3-12 times higher than normal to allow the person to have some in their system for a while as they wean down. The nurse walked out of the room for nearly 20 minutes and had not told my wife that she had switched the machine.
My wife self-medicated three times on what we later found out was nearly 10 times the normal dose. She passed out and was out for nearly 10 hours. Of course, she didn't get to see the boys that day. There were, fortunately, no after effects. She wore it off well. But, the nurse was fired. And she should have been. Had my wife been conscious enough to hit that button one more time, she may have not made it through it, or been permanently harmed. My wife was on the maximum dose allowed at the time.