Mental states such as loneliness, compulsion, anguish, attachment, pain, and faith are not just "all in the head" but in the brain as well. Brain, mind, and body are a continuum. Our thoughts-intention, fear, images, suggestion, expectation- alter the brain's chemistry. And it works both ways; thoughts can be altered by changing the brain's chemistry with drugs, nutrients, oxygen. The brain is hopelessly complex.