short and simple terms its being sensitive to others pain a common example is when someone is in labor and their loved ones are so in touch with that persons pain that their body reacts by maknig the person feel the affects (in other words having false labor pains when someone is really in labor)

another example a tooth ache one person has a tooth ache and the other person is so sensitive and close to that person that they "perceive" their self as having the toothache too.

many people with mental disorders ......sometimes.... can "take on"or perceive their self as having the same mental problems as another. here in my location another term for this depending upon other accompanying symptoms is ......sometimes....called fictious disorders