If enough psychologists and civil servants wanted to, they could have you declared insane, and then nothing you say can come to your defense as you are now deemed too insane to be listened to. I know this isnt as straight forward as the average person thinks, but the possibility of it even happening once to someone is terrifying.

Oh that and trigeminal nueralgia, the worst pain possible forever.

A lot already mentioned, so those too, but also:

Rogue black holes. Just thinking about them makes my guts queasy.

Snake clowns!

transmissible cancer, some surgeons had got cancers from thier patients by accidentally pricking themselves with a contaminiated instrument, although it was treatable and non issue once the tumor was removed. other forms like transplant patients is another source. rare t-cell cancers like mycosis fungoides, you go from patches, to “plaques” to tumors.

and there has only one case of animal to human cancer, the guy had AIDS and got tapeworm cancer from it, which is the most unusual situations out there.

Abuse of the psych. bug that leads to faschism by smart evil people that know exactly what they are doing and somehow make it work stable for centuries.

Not having any feeling in your legs, but not being paraplegic, so you could legit accidentally walk outside without any pants on.

Dying painfully

Some form of torture. The thing about torture is you can always add “and then…”

Psychological and physical

Imagine being forced to rip off your significant other’s fingernail.

And you might say “There’s no way I’d do that”

Sadly you will. Either to save yourself or them from more torture.

You will do it, we all would. That’s scary.

Nice try, sleep paralysis demon

alzheimers.

Mondays

On the smaller scale it’s probably my wife and dog dying, in the larger scheme of things it’s the rise of fascism here in Germany and Europe.

The sun moving the other way through the sky

Dick spiders.

More seriously: body parasites of any kind.

Prions - Actually nightmarish.