I'm not sure if this is what you're searching for but...

I once had horrible food poisoning and went into the hospital emergency room. (actually, after going to the first hospital and waiting for 2 hours and pulling some of my hair out because of the pain, I was able to be driven to another hospital and get in in 10 minutes). The pain was some of the worse pain I've ever experienced.

The doctor gave me morphine in an I.V. and the pain was gone literally in seconds. I felt really relaxed and peaceful. It was such a dramatic experience and a dramatic change in such a short period of time that I never forgot the experience. I even asked if I could have another shot the next day (looking back, I can't believe I did that). They gave me one but this time in the bum (as the English say). (That's not a "bad" word in England, is it?)