Why does global Metta cause overwhelming empathy and compassion fatigue?

As the practice is extended in such a way that the global suffering is involved, I experience a feeling of total pain and hopelessness and this takes in all the negative energy. I am drained emotionally by this high level of empathy. I am concerned that Metta is bringing about compassion fatigue and spiritual burnout, which directly aggravates my underlying depression and anxiety. Is it preferable to establish stringent emotional context and express love to the inner circle only? My name is Tanmay, from Hyderabad. DOB: 14th June 1987. Time: 3:10 PM.