I'm writing a book now about a guy who drinks very heavily; I don't think I've ever had a hard-drinking character (though I've had sober characters), because when you write somebody who drinks a lot, you also need to convey the upside of drinking. It can't all be vomiting and sadness! There's a majesty (at least on the inside) to real drunkenness and real alcoholism, and if you can't get into that, then all you've done is pathologized your character and stripped them of their individuality.
Anyway, so this character drinks very heavily, and I feel like I'm starting to get into their heart of longing, because when I write, things come up. I'll be writing something, and suddenly I'll be able to feel things from my drinking days that I'd forgotten up until this moment. Little bits of sense impression, fragments of feelings, and other detritus.
I don't think that our brain stores memories haphazardly. I think it only stores things that are connected to deep emotions, and when things start coming back to you, then you know you're beginning to touch on those emotions.
(Yes I am doing a little writing on my honeymoon. What, am I supposed to quite entirely for two weeks?)