One interesting aspect of alcoholism that is both taught and experienced in AA is the progressive nature of the disease. One can lay off drinking as did Don (for only ten days), start up again, and be face down in the gutter again in a matter of days, even if the lay off was for months, years or even decades. It's a common recovery fallacy that "I'll just take a few weeks (months, years) off and be good as new and pick it right back up again. Bad idea jeans as they say.
Four days is not enough time to really screw up a non-alcoholic, but it is plenty of time to get a real one back in the groove and as f'ed up as they've ever been.
Nah, I don't buy it. Don Birnam is 33 years old in the movie, and 4 days of drinking would not give the effects shown in the movie. Full-blown delirium tremens would not manifest itself there and then, as it does in this movie. Perhaps if he was over 50 and had a history of heavy binge drinking off and on for half of that. Tolerance builds itself up over years, even decades, and it is not until having been drinking for about 20 years, that it decreases again. Then it reverses and you can tolerate less and less alcohol.
On the other hand, in real life, he probably wouldn't have stopped after those 4 days, but rather thrown himself at the opportunity of drinking more alongside with Helen, when she offers him it at the end. Then, he would probably persuade her to lend him some money to go buy another bottle. The next day he would really hock his typewriter and buy some more.
The timespan of 4 days is the most (only?) unrealistic aspect of this movie. 14 days would be way more credible.
Peter Laughner of Rocket From The Tombs drank himself to death at 24 (Pancreatits)
Pigpen from The Grateful Dead drank himself to death by 27 (Cirrhosis)
Know we're not necessarily talking about the same effects on the body, but I don't think his age matters that much. As my example says, some people can cram an incredible amount of booze into a short timespan.
Don't be fixated on the 4 days. It's just a small segment of the character's life. Look at the bigger picture. No one consumes, and is desperate, as Don is with drinking 4 days.