Both times that I was recovering from hernia operations, my blood pressure dropped dramatically. It happened in post-op each time, but not during the operations.
The first time it happened, about 20 years ago, I was simply told about the severe hypotension. The nurse didn't seem overly concerned, though. I remained very weak long after the nurse said that I should've "recovered by now", and it was hard to keep my head from flopping down as their staff was wheeling me out of the hospital to my parents (who were the transportation).
The second time it happened, about 10 years ago, the nurses in the post-op room mentioned my extreme hypotension and that they were worried about losing me. On that occasion, I felt COMPLETE BLISS before the screams of a nurse finally penetrated my mind. It was like her yelling was barely heard initially, increasing in volume until it reached maximum volume and annoyance for me. I briefly opened my eyes at that point, but quickly closed them again while hoping to return to the wonderful feelings. That's when the yelling nurse continued being loud, tapping my cheeks, and scolding me for "being bad" in regard to closing my eyes. So a return to the bliss was totally impossible. That hospital kept me for "observation" for many hours after I assured them I was fine now, so my poor niece (transportation) finally got me out of there by early evening instead of the morning as she'd anticipated.
I never died, however -- i.e., I never lost brain function. So I attribute the intense feelings of joy to my own brain, but I don't know why my brain reacted to the hypotension that way.