This is currently unanswerable as there is still so much to learn about neural receptors. For example, by reference to only one of the opiate receptors, the mu receptor, it occurs pre & post synaptically & in various areas of the brain.
It is activated by means of a g-protein second messenger signaling system which is itself a complex pathway involving activating & inhibitory enzymes & other proteins all of which are impacted by individual biochemistry, diet & other chemicals in the blood stream. Not to even mention the placebo effect whereby we all anticipate a response from a drug, even if only subconsciously.
I agree that it's a fascinating question though.
HI welcome to the forum....sorry no doctor on on this forum but narcotics effect people in different ways I got a very sleepy euphoric feeling from the same thing that gives others bursts of energy I guess it just the way your brain is wired wish I had more for ya but I dont even think science can enplane this fanamana .........Gnarly
I have read on it, but I am not going to try and explain as I don't have the information right enough to the point I can tell you.
If you want to get that answer here, just please give it a while, people will answer.