An empath is someone who experiences some of the same emotions and feelings as others that are close to them. In some cases, this means those who are close to them physically and, in other cases, it means those they are close to emotionally. Some empaths feel many different emotions from others, but many only feel certain emotions or feelings, or feel them only when they are strong. It is especially common between twins and between mother and child.
    I mostly feel the aches and pains of others. I remember once, quite a few years ago, I was in the office with my boss and he gave me a strange look and then said that the arthritis in his hands was really bothering him that morning. I didn't realize until he said that, that he had been rubbing his hands as if they were cold and he was warming them and, without realizing it, I had started doing the same because my finger joints were aching when I was near him. And once, when I donated blood to the Red Cross, the elderly nurse who took my blood must have had arthritis bad because my joints ached for hours afterwards.
    I also seem to pick up on sadness easily. I remember another time that I took my mother to the funeral of someone she knew, but I didn't. Even though I didn't know the person, I got very sad by absorbing the sadness of others there. 
    It really doesn't sound like being an empath is a pleasant thing, and it isn't, but useful things are not always pleasant. Being an empath has been useful to me because sometimes, when one of my dogs is sick, I can tell to some degree what is wrong because I will feel the same symptoms. More importantly though, feeling others pain and sadness helps me to be more sympathetic to others. You can't help but sympathize when their pain is your pain. That is why some degree of empathic sensitivity is very common in those developing their spiritual side. We need to know that we don't stand alone, we are part of the One, we are all connected. And that is one reason why highly developed spiritual people have to limit their contact with the general public. The bombardment of aches, pains, and generally negative emotions that hit them in such circumstances can be overwhelming. When they do make a public appearance, they often have to put up an emotional shield for protection. This may make them seem somewhat aloof, but they are not.