i) we are designed to be social/active, excluded from social activity life sucks.
ii) we are designed to be loved, excluded from love life sucks.
iii) we are designed to have a functioning immune system, when its compromised life sucks.
when the above is positive life is positively inclined and such thoughts are unthinkable, when the above is negative life is negative and such thoughts are thought about. its a stress response to the environment, social and internal system as a balance to the way you experience situational life. the mind body connection.