Emotional Contagions: Emotions are contagious like viruses

Emotional contagion is defined as "the tendency to automatically mimic and synchronize expressions, vocalizations, postures, and movements with those of another person's and, consequently, to converge emotionally". From that, the theory is that passive stress, and other emotional states, can be as contagious as a common cold and that we can catch other people’s stress etc if they are exposed for long enough.

Studies have apparently shown that emotional contagion does occur in groups and changes people’s moods. It suggest that although most of the time we think we are acting out of our own volition and in our own best interest, in fact, we are merely reacting to someone else or aligning ourselves with groupthink.

Emotions are contagious ... from Emotional Contagions by Elaine Hatfield, Professor of Psychology, Richard L. Rapson, Professor of History and John Cacioppo, Professor of Psychology, and The Ripple Effect: Emotional Contagion and Its Influence on Group Behavior by Sigal G. Barsade, Yale University.

People seem to be fully aware that conscious assessments can provide a great deal of information about others. They seem to be less aware that they can gain even more information by focusing-in now and then on their own emotional reactions during those social encounters. As people nonconsciously and automatically mimic their companions' fleeting expressions of emotion, they often come to feel pale reflections of their partners' feelings. By attending to this stream of tiny moment-to-moment reactions, people can and do “feel themselves into” the emotional landscapes inhabited by their partners.

... there is evidence from animal researchers, developmentalists (interested in emotional contagion, empathy, and sympathy), clinical researchers (exploring transference and countertransference and the impact that anxious, depressed, and angry people have on others), social psychologists and sociologists, and (most recently) historians, which suggest that people do indeed often catch the emotions of others.

We sense our 'individuality' in modern life, but this is only a recent development - a few hundred years. For most of human history, people have gained personal identity from a close nit community based on an emotional connection to religion and mythologies. The need for connection and therefore the power of the group is deep in our psyche - we are influenced without even being aware of it particularly if we are unsure of ourselves. It takes courage to step away from the influence of others because influence, as it has been through history, is often fear based.