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In Mental Health
What is emotion?
Much discussion revolves around a clear definition of "emotion" and "feelings". Research by Robert Plutchik has greatly clarified it, but most would agree that any emotion mus…t be a state of mind and body. And as a person becomes aware of a change in the environment (such as the arrival of a predator), the person may have significant changes of state within the mind and body which are measurable -- perhaps a racing heart or a sinking sensation in the gut..
Since everything in the universe is considered to be a form of energy (the 1st law of thermodynamics), then emotions and feelings must also be energy. And if we can recognize a difference between such sensations (love is not hate, happiness is not sadness), then the distribution of energy within the mind and body must be different. Thus, changes in emotional states must be changes in energy states - either in the amount of energy being distributed, the directions it is distributed, or both..
Evidence seems to point to two main states of distributed energy: balanced and imbalanced. With a balanced state, the body and mind work harmoniously, and we feel great. But imbalanced states are recognized as illness or stressful (we feel bad). The balanced state strongly correlates to the parasympathetic nervous system (PNS) which becomes dominant during sleep and rest. Concurrent with the PNS, the immune system is facilitated. Meanwhile, an imbalanced state strongly correlates to the sympathetic nervous system (SNS) which becomes dominant during "fight or flight" situations. And the immune system appears to be suppressed during such times of stress. Evidence shows the prolonged stress invites disease and even death (see research by Allen Rechtshaffen)..
The reason for two main states seems tied to limited resources. We can only run so fast, climb so high, or work so hard. Thus, we have physical limits. If we are being chased by a predator, like a lion, then it would help us survive if we maximize our resources toward fleeing the lion. Issues such as "catching a cold" or "digesting lunch" seem to be much lower on our list of priorities while running from a lion. If our energy resources are diverted from those lesser priorities, then we can maximize our response to the urgent need at hand. So, the imbalance is a mechanism to conserve and maximize energy used for escape. Since we do not know how far nor how fast we must run, "stockpiling" whatever energy we have seems prudent for survival - even though it doesn't feel good at the time..
So, "feeling good" appears to be a balanced and healthy state of the mind and body. "Feeling bad" appears to be an imbalanced state and unhealthy for us (unless it helps us escape from a lion). ( Full Answer )