What I think he meant was that lorazepam isn't a painkiller and it isn't use to treat pain. From my understand, doctor use other drugs for pain medication, not propofol or lorazepam. From what I read of propofol, you can appear to be sleeping and non-responsive, but you are still 'conscious in some sense and can feel pain.
Also, I don't see him discrediting Shefer, but he just doesn't agree with him on certain things. Like how he thought the sleep study was interesting while Shefer was very critical of it. This kind of disagreement happens all the time in any profession.