There are a few prion diseases that are absolutely horrible. I believe one of them causes you to be unable to sleep until you go mad.

Alzheimer's. The thing I fear most is that I will die surrounded by a bunch of people I don't know, feeling scared and alone. I'm terrified of forgetting who my loved ones and my family are. I don't want to go like that.

This is where physician assisted suicide has a really strong case.

Anything that makes you aware that you're slowly losing touch with reality and control of your body or causes you to mistreat the people who love you.

There are so many things that would be fighting for last place honestly. Idk, being stuck deep in a cave Nutty Putty style for days, barely able to breathe, arms pinned totally by my side, legs all twisted, total darkness. Slowly suffocating as the blood pools in my head and I become delirous.

That terrifies me so much. But idk, there are so many horrific ways to die. There are many cases of people being tortured to death over weeks or even months if they somehow survive that long.

There are also a bunch of diseases that are all around awful and terrifying. That syndrome where you are trapped inside your own body, total unable to move anything but you are aware of everything around you, maybe would be the most horrific.

Idk, too many horrible ways to suffer and die in this world...

I think I may be an outlier here. I really don't want to die in a sudden 'didn't-see-it-coming' kind of way, like getting hit by a semi or a freak accident with heavy machinery kind of way. The idea of going from living, thinking, feeling, person to chunk(s) of meat in an instant terrifies the shit out of me. Especially if it's caught on video and people watch it for laughs or whatever possesses them to watch that kind of thing.

Don't get me wrong, I don't want to die in some slow, painful way either, but something I had some agency in would be worlds better. Like taking a bullet to save a loved one, or punching my own ticket after getting a terminal diagnosis, or even just taking a deliberate, calculated risk.

Dying at work.

These people have already taken damn near everything they can from me. I'd rather kill myself right now than find out I die at work.

Well if we exclude the slow and painful ways to die I'd say that drowning by diving under ice and not finding the way back. The panic on your last minutes must be something else.

My biggest fear, given mental health issues, wondering through out life if I'm going insane, seeing things, hallucinating, etc...

I'm terrified that the moment of death, I won't be able to tell if it's real or not. So it will be an infinitely protracted moment, and right now, I may already be in that moment.

Where the F are serious mental health conditions? When your appearance seems intact from the outside, but inside your reality slowly yet steadily derodes, and there's no way to help it. Going insane. That's for me the last one. Prefer physical pain over losing touch with reality.

For me, it's any situation where you know you're fucked but can't do anything to stop the inevitable.

Give me instantaneous death where idk what happened or a slow progression of disease where death would eventually be a welcome relief. It's the in between that freaks me out.

Lathe accident.

Idk, but bone cancer looks like a bad way to go.

Some kind of dementia. It's a cancer of the soul which arbitrarily removes parts of you that you can't even perceive the loss of. I had an MS patient whose vocal processing was reduced to the point that he could only say variations of "you fucking bitch". He was totally bed-bound and dependent on a mostly female nursing staff for every single need. Most of those employees were burned out and he could only communicate to them using a wildly misogynistic slur. I've seen it reduce a famous AIDS researcher and a WW2 pilot to toddlers, others to cornered raccoons, for some it's a nightmare they can never wake up from and they just spend all day/night reliving their worst memories. For a good 10% on the ward it just takes away their executive function and they can no longer control their worst impulses or recognise that they should.

Cancer and strokes are a close second for more or less the same reason, but dementia is so existentially terrifying to me.

Being eaten alive by animals

Being buried alive.

Alzheimer's.

Milk and honeyed to death, if you know it, you know that shits barbaric.

If we talking in the realm of realistic and probable, probably Alzheimer's, or maybe being trapped in a vegetative state but concious and lucid.

Rabies is my first thought as well, by the time symptoms show up and you go to the hospital, there is nothing you can do other than die in horrifying confusion, fear, and panic as your brain melts into mush.

Radiation illness is one of them, there are certain yields that make it rather nasty. Rabies is also pretty high up the list.

Mechanically wise I remember the OSHA case of the worker getting trapped in a walk-in autoclave and literally steamed to death. because that actually takes a long time.

Prion diseases and locked-in-syndrome are also pure horror.

Least preferred way in the disease category would be any disease that slowly erodes the mind and body. Being unable to move or know where I am, who are those around me sounds terrifying, not to mention the burden (financial and emotional) it would be on my family. No thanks.

Now for "mechanical" I'm not totally sure what this means but a similar logic applies. Of the classic methods of execution I think getting burned alive would be probably the last choice, but I'd take that before slow torture that's for sure

Water

Dying from poisoning with Dimethylmercury, which happened to one scientist and it’s like an Alzheimer’s speed run but you don’t see it coming.

Being wrapped tightly in untreated canvas, soaked in hot water, and then the canvas begins to shrink.

It’s easy to become desensitized to, since many of us see crosses frequently, but death by crucifixion is absolutely horrible.

Wood chipper, feet first, slow setting.

Easy: drowned in spiders

Blood eagle, iron maiden, rat torture (method where rats were placed in a container and heated, forcing them to gnaw through the victim's body to escape), brazen bull, lingchi.

Or anything from the spaniah inquisition

fire or drowning probably

Rats and a heated bucket against your stomach

Fatal Insomnia.

Brain eating amoebas

I guess the sandpaper room would be pretty far down on the list.