Mother always told you, "Put your jacket on, you'll catch pneumonia!" In Real Life, exposure to the cold weakens your immune system, and damages the cilia in your respiratory system that sweep the microbes away from your lungs. But you don't always get sick in bad weather, especially if you're a healthy twentysomething. Moreover, in real life infections have an incubation period. Symptoms usually don't appear right away. This tends to happen very early in a relationship, shortly after the couple meets for the first time. Examples of Instant Illness include: