Sickness

Villagers in Animal Crossing: Wild World can become sick and remain so for the rest of the day, at least. While they are sick they may shiver or have the "depressed" emotion. 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. Sickness lasts a variable amount of days. While villagers are sick, they will not react positively and a new option appears at the top of the interaction menu, "Need medicine?" Selecting this will prompt anger if the player does not really have medicine in his/her pockets but will open the pockets if s/he does. After receiving medicine, the villager will thank the player. After the sickness passes, the villager will give the player an item if s/he took care of the villager while s/he was sick.

Glitches associated with Sickness
If the player is to open his/her town gates and have a guest come while a villager is sick, then that villager is instantly better.