Alcohol.
I've probably told this story enough that everyone just rolls their eyes now, but a few years back me and my boyfriend were both homeless alcoholics. I knew that going cold turkey from alcohol was really dangerous but I let him convince me anyway as we'd TRIED to like slowly taper down and couldn't. So we saved up to rent a hotel room for a week to just stay in bed and try and relax while withdrawing. I managed to get a few hours sleep in the early hours in the morning of day three and when I woke up he was lying dead on the ground. Apparently, he'd gotten up in the night to use the bathroom and had just had a massive grand mal seizure and passed away.
I've had many horrible experienced with alcohol withdrawal, inc. resulting in permanent injury/disability:
I'd not even quit cold turkey, just decreased how much I was drinking. I was watching TV and then suddenly I was sitting on the living room floor with no idea how I got there from the sofa. Also my mouth REALLY hurt. Just as I was becoming lucid and realizing that I'd a) had a seizure, and b) bitten a significant chuck out of the side of my tongue resulting in the pain and also my face and shirt being covered in blood, my dad came home, saw the state of me and took me to the emergency room.
I'd been there a couple hours when the doctor called my name. I remember getting out my seat and walking across the room, then...nothing for 2 days.
Apparently I'd had another (much worse) seizure then. It went on for over 5 minutes and I didn't breathe during it [not sure if it's normal to stop breathing during grand mal seizures or not] which obviously resulted in hypoxia and I have mild-moderate brain damage from that. They said I definitely would have died if I was extremely lucky to be literally in a hospital when it happened. They gave me two doses of (I can't remember if it was Diazepam or Lorazepam) and I still didn't come out of it, so they had to put me into a medically-induced (barbiturate) coma to stop it.
It was also so violent that I fractured my orbital socket, dislocated my shoulder, cracked a bone in my wrist and broke 6 ribs. I also slipped two discs in my back, which have been gradually getting worse since and have now devolved into two herniated discs which cause severe enough pain to require me to take Morphine every day.
This

, even in a Hospital they don t actually seem to have a clue how intense.
Strong seizure s are, had em too from stress, 2 year insomnia and drinking evt too.
In the Hospital they failed to stop em [seizure/ Ictal psychose],
with their ini mini benzo doses. Just temp came out.
"Here is your phone call your Mom your OK,
and she can come and get you."
Boom, another seizure.
Suckers don t even practice medicin any more.
In a Hospital crazy but true.
When a few hours ? the out side hired psychiater arrived.
100 mg Diazepam equivalent + Haldol got me out,
only time i was awake on 5 fold dose of Diazepam,
would normally put me under. Now walked to my bed awake,
and glad to be back and alive. fuckers thinking back.
i even swallowed my own vomit, outta respect !
So that no one had to clean my mess, just to discover they
totally fucked up treating me, they wanted to sent me home.
In between seizure s the dimwits.