This War of Mine: Final Cut

This is best to do with a long custom game, no winter and low conflict. Once a person becomes slightly ill, make sure to keep them hungry and make them sleep on the floor or have them scavenge. Sometimes the person recovers on their own, so may need to try multiple times. They should then go from sick then to severely ill. I found that they can sometimes die if they are mistreated when severely ill, so once this occurs, make sure they are well fed and sleep in a bed each night (very important, no meds). When they are untreated without medications, they should eventually become terminally ill. Once this occurs make sure they are fed a cooked meal(s) until full, take medications (not herbal), sleep all day and all night in bed. Also keep someone on guard during night while this person is sleeping. Each day repeat this and they should eventually recover back to normal and achievement should unlock.

You need to recover from being terminally ill. When you get someone who's sick try and keep them out of bed and don't give them any meds until they are sick enough. Once they are give them the good pills for a few days and keep them in bed.