If you talk to a believer in out-of-body experiences, this is the case they'll cite as evidence. The BBC even made a documentary about near-death experiences that directly references it. Unfortunately, the most likely explanation is less supernatural but more alarming: anesthesia awareness.
According to studies, about one in every 1,000 surgical patients wake up to some degree under anesthesia, experiencing some form of awareness while their surgeons are digging around inside them. In Reynolds' case, she had trouble remembering her surgery after a certain point, and it turns out that point was the moment her brain was shut down. Everything else could've easily been a case of overhearing sounds during anesthesia awareness, and her brain filling in the details later. As for remembering specific things (like the saw), it's not like those tools only existed in that room. Hearing the noise it made would have let her mentally picture it if she'd seen similar gadgets anywhere else (on TV, at the dentist, etc).
Then there was apparently some encouragement on the part of the staff. In Pam's own words, "I thought maybe it was my imagination and I had a dream, but they told me that this was not the case and what I saw really happened ... They kept telling me that it was not a hallucination."
We're not casting aspersions on the surgical staff here, but hypothetically, if we were surgeons and one of our patients told us they remembered details of the surgery, we'd try to tell them it was an out-of-body experience too. Letting them think they've just experienced evidence of the soul is a hell of a lot better than saying, "Oh yeah, sometimes our anesthesia doesn't work at all and the patient is helpless to do anything about it. Tell your friends!"