Villagers in Dōbutsu no Mori e+, Animal Crossing: Wild World, Animal Crossing: City Folk, and Animal Crossing: New Leaf can become sick and remain so for at least the rest of the day or so. While they are sick they may shiver or have the "depressed" emotion, until the last day of sickness where they'll seem fine and not depressed, but they'd still shiver. Villagers can be recovered from being sick for the remainder of the day (up until midnight) if they are given medicine from Tom Nook's shop. The sickness lasts a variable amount of days, from one day to two weeks. While villagers are sick, they will not react positively and new options appear at the interaction menu, named "Need medicine?", accompanied by another option named "Are you OK?" Selecting the "Need medicine?" option will prompt anger if the player does not actually have any medicine in his or her pockets but it will open the pockets if she or he does have medicine. After receiving the medicine, the villager will thank the player. After the sickness passes, the villager will give the player an item if they took care of the villager while they were sick.
If one player gave the medicine to a sick villager already, and another player talks to that villager, then the sick villager may be implying things like "<player who gave medicine to villager's name> is my hero!!" followed by an angry emotion, or maybe "I've got one person to thank for my health: <player who gave medicine to villlager's name>!" appearing with two different options like "Take care!", "G-R-O-S-S!" "Uh, adios!" even though if the player selects "Take care!", then the sick villager might say things like "Hey, thanks for worrying! You're a true-blue bud, <catchphrase>!" followed by a blushing emotion, even if that player was not the actual player who gave the medicine to the sick villager. Because of this, only one player may give the sick villager medicine.
Sick villagers usually send the player a letter of thanks once they are better. However, some villagers may send the player a letter even if they are still unwell and have only received medicine once.
Sickness in Animal Crossing: New LeafIn Animal Crossing: New Leaf, symptoms of sickness are more cold-based, and are actually referred to as colds. On occassions, a villager may be sick for more than one day. Dark clouds (depression) and shivering (fear) are still there, but the new emotion "Sneeze" is used now, and sneezing is slightly more frequent in conversation. Prior games did not have this emotion, but instead, made do with a brief burst of the "Anger" emote overtop the Animalese vocalization of a sneeze, which would shake the dialogue box. Also, if someone in town is sick, other villagers will know, and will sometimes tell the player that "X has a cold" and that they should go see how they're doing.
Additionally, if you get stung by a bee while a villager is sick, talking to other villagers will result in some of them giving you medicine. This can be useful if your Nooklings' store is closed, you don't want to pay for medicine, or if your current store is a Nookling Junction.
Glitches associated with Sickness
In Animal Crossing: Wild World, if the player is to open their town gate and have a guest come while a villager is sick, then that villager is instantly better. This was fixed in Animal Crossing: City Folk, as the character will lock their house, leaving a sign saying that they are feeling ill.