The Drinker

Fallada is a pseudonym for Rudolf Ditzen, who wrote several international bestsellers before the Nazi rise to power. He wrote The Drinker while imprisoned in an insane asylum after going on a huge drinking binge. The back cover of the book claims the text was encrypted, but he was actually just writing overlapping text so as not to use up his paper allotment.
Herr Sommer runs the main grocery business in a smallish German town, slowly becoming estranged from his wife who was the more efficient business partner who drove most of the contracts he’s coasting along with now. When he loses the main contract, he’s too ashamed to tell Magda (his wife), so he rambles through the countryside for a long walk, ending up at an Inn to quench his thirst, first with beer, then schnapps, which begin his spiral into drunkenness.
The book clearly lays out how an obsession with something (drink, drugs, etc.) will put you in a delusional state where only the very next moment matters. He eventually steals 5,000 marks from his bank account, is caught in the act of burgling his own home for silver, clothing, and threatens to kill his wife. This death threat becomes the pretense needed to clap him in irons, whisk him into the prison system and eventually to the insane asylum.
According to the dates of the manuscript it took him two weeks to write. Wikipedia tells me that he wrote his last book Every Man Dies Alone in 24 hours.

I stared at the paper for a while, then went to the window. Outside autumn was drawing on already – swaths of grey mist drifted across the countryside, I saw the first early potato-pickers among the rows. “Autumn is coming,” I said to myself. “That’s bad.” I did not know myself what I meant. I only knew that I was in a bad way, very bad. Two lines from a poem I once read, ran through my head: “This is the autumn, it will break your heart.”
Obstinately, they returned, they kept returning with a desperate obstinacy.
“This is the autumn, it will break your heart.” Two words tacked themselves on: “Fly away! Fly away!”

This is the autumn and it will break your heart.