Emotional Contagion
The automatic spread of an emotional state from one person to another through mimicry of facial expression, tone, and posture, largely below conscious awareness.
Emotional contagion is the mechanism thought to underlie much of affective empathy: watching someone smile activates some of the same facial muscles in you, watching someone flinch activates a mild version of the flinch, and the physiological state that goes with the expression tends to follow.
It explains why a tense meeting stays tense even after the original cause is resolved, why a calm interviewer can steady a nervous candidate, and why one distressed person in a room can shift the mood of everyone in it before anyone speaks. It is involuntary and largely unconscious, which is what separates it from perspective-taking — you cannot simply decide not to catch a mood the way you can decide not to imagine someone's situation.