Empathy is very tricky feeling. The standard meaning tells that empathy means 'ability to understand the feelings of another being', Sympathy means 'feeling of pity and sorrow for someone else's misfortune. Many times what we do is we try to slipin into someone's shoe without removing our shoe !! and think we are empathising with the person. In the first place removing our shoe is not very easy. It needs lot of 'Self Awareness'.
One guiding factor can be if you are really empathising with person, if will never get a feeling of pity or sorrow, on the other hand you will feel very humble and be thankful to the person who gave the opportunity to you to Empathisewith. It is a rare, special feeling.