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The psychic tears are one of three kinds of tears produced by the eye; the first two being for keeping the eye moisturized and clean respectively. The psychic, or crying, tears are produced by strong emotional reaction you experience from stress, pleasure, anger, sadness, and suffering to indeed, Physical pain. These tears contain a natural pain killer named leucine enkephalin. (Perhaps that's why we feel so good/tired after a good cry)

The "Crying" tears are linked to the brain via the nervous system. More specifically the autonomic nervous system that controls the heart and other functions you do not control. So when you have a cry your emotions force your body to take actions. The tears are only one part of the reaction, All of this is linked to the fight or flight instinct all of us have. Your heart increases, your breathing becomes more difficult, you sweat. All that is linked to the emotional and psychological aspects of why you cry. Heck even the verbal call of a cry is a psychological signal to others saying "something is wrong come help me."

So in short. Our tears are our fire alarms for our body. Without them firefighting teams would never know when to help. and you would never know when your body is reaching critical levels of physical, social and emotional stress.

Just an FYI – it also purges stress hormone. Through your eyes. Liquid stress.