interestingasfuck

Okay, so there's two main reasons why alcohol withdrawal is so brutal (much of what I'm about to say also applies for benzos too)

1.) Alcohol primarily increases the actions of a neurotransmitter called GABA, which is sometimes referred to as "the off switch of the brain" because of its role as the key inhibitory neurotransmitter. If you've ever heard people say that alcohol is a depressant, this is what this means (although people often use that to mean it will make you emotionally depressed, but that's not what the phrase means — it means that it's a central nervous system depressant. Certainly alcohol (and alcohol withdrawal) can affect mental health, but as a biochemist, that's far out of my wheelhouse; I do know that the effect is not a simple one of "alcohol makes you sad").

Chronic alcohol dependence means that the brain has to upregulate a bunch of systems, in order to compensate for the neuronal inhibition caused by extra GABA activity. It's basically the same phenomenon as how if you regularly drink caffeine, it will stop being effective due to compensatory upregulation of the system involved — except when you stop drinking caffeinated drinks, you're mainly feeling the impact of that one upregulated system. It feels awful, but it won't kill you. However, GABA has such a far reaching impact across the entire central nervous system that when you stop drinking, your entire brain is running at an increased level of excitation — which is what can lead to things like anxiety, tremors and seizures.

2.) Another reason why alcohol withdrawal has such a big impact is because alcohol doesn't just affect GABA, but many other neurotransmitters. It's what my neuroscientist friend referred to as "a dirty drug" (n.b. there's no value judgement in this statement, it's just just referring to it being less specific than other drugs). Dopamine, serotonin, glutamate and norepinephrine (and others) are also affected by alcohol consumption, and as with GABA, chronic alcohol dependence causes these systems to adjust their level of activity to compensate for the alcohol. When a person stops drinking alcohol, it's basically all of these compensatory mechanisms being suddenly revealed.

Below is a diagram that shows how chronic alcohol dependence affects neurotransmitters (an up arrow to the left of a neurotransmitter means that it is upregulated due to alcohol (i.e. systems involved become more active), and the symptoms on the left are the result of the changes to those systems, only revealed during alcohol withdrawal. I don't expect you to be able to follow the specifics of this image, given that even in the textbook I got this from^[1], the main point of this image seems to be to go "There's a heckton going on and everything is so interconnected that it's super difficult to figure out exactly how alcohol withdrawal causes these symptoms"

[1]: citation for the image: Howard C. Becker, Patrick J. Mulholland, Chapter 9 - Neurochemical mechanisms of alcohol withdrawal, Editor(s): Edith V. Sullivan, Adolf Pfefferbaum, Handbook of Clinical Neurology, Elsevier, Volume 125, 2014, https://doi.org/10.1016/B978-0-444-62619-6.00009-4. (https://www.sciencedirect.com/science/article/pii/B9780444626196000094)