Emotional contagion
Overview
Emotional contagion is the phenomenon in which coming into contact with someone else's expression of emotion makes you unconsciously experience the same emotion. It is a concept systematized in 1994 by Elaine Hatfield and colleagues. When you're near someone who is laughing, you start smiling too, and when you're near someone who is angry, you get irritated too. Unlike conscious empathy, this happens automatically and unconsciously.
Face to face, emotions spread through facial expressions, tone of voice, and body movements. In text communication too, emotions come across through writing style, word choice, punctuation, and emoji. Even if emotional contagion through text is weaker than face to face, it does exist.
Emotional contagion in a question box
In a question box, emotional contagion can happen in a chain. For example, reading a question with an aggressive tone puts the person answering in a bad mood. An answer written in that state unconsciously takes on a prickly style. Followers who read that answer also end up feeling vaguely uncomfortable. One aggressive question, passing through the person answering, can bring down the mood of all their followers.
There's also the opposite pattern. Reading a warm question lifts the mood of the person answering, their answer takes on a warm tone too, and readers feel good as well. The atmosphere of a question box community is also shaped by this buildup of emotional contagion. Each question and answer affects the emotional coloring of the whole community.
Managing emotional contagion
Because emotional contagion happens unconsciously, you can't prevent it completely. But by being aware of it, you can reduce its effect. Recognizing after reading a nasty question that "My mood is dropping right now. This is emotional contagion" makes you less likely to be dragged along by that emotion.
A practical countermeasure is not to write an answer right after reading a nasty question. Letting time pass can make the emotion you caught fade. Arranging the order also helps, such as reading positive questions first before you write answers. Get yourself in a good mood with good questions, then take on the difficult ones. It's a strategy that turns the mechanism of emotional contagion to your advantage.