> In fact, this effect was so powerful, that the "come thru" message from my dealer, and driving over to his, would make my withdrawal symptoms subside nearly entirely, well before I'd actually taken the drug.

https://en.wikipedia.org/wiki/Reward_system#Anatomy

Though I've not read any articles on heroin or these long lengths of time specifically, opitates are known to have these anticipatory responses in the brain like the one you describe.

Brains are indeed totally crazy.