Status: Screwed

Here's something fun to think about: what is the worst status effect - asides from the obvious K.O. or equivalent dead status - in a video game you have been inflicted with? What makes it worse than other status effects in other video games?

Damage turns into healing. In RTS this is a death sentence really if you have nothing that is immune to this status effect cause your entire deathball turns into a healball meanwhile the enemy can deal damage to your units so you're basically a sitting duck healing them while they kill you.

Cursed from Dark Souls 1.
If you get cursed, which is very common with certain enemies, you instantly die, which, like you said, is the obvious instant KO. But then, it doesn't stop there... Your total health is halved until you use a fairly rare item to cleanse your curse. This persists through death. If you don't have one, well.. enjoy navigating your way through hordes of enemies as you backtrack to one of the semi-well hidden vendors that sell one, and then get to fight through those hordes of enemies again.
It's not as bad if you're a veteran player because you can just buy a few in preparation, but if you don't know about curses or even know where the NPCs are that sell the item to cleanse them, then have fun!