What is the cause of disease? What is the connection to personal conditions built up in ones life?

The cause of disease in my observation is anger ,fear,and hatred.If we can let go of these negative energies we are disease free. I befriend a lady that has cancer,she is consumed of anger. So I let go of my anger on any one who oppresses me,because I am vain of my . I find out that the greatest medicine is our mind to heal our self. When I was in a car accident,I don't want to take pain killer,my belief is it will impaired my mind so I kept saying over and over "my mind is stronger than my pain more than a 100 times until the pain subsided.