How we, human, feel sense of happiness? 
The sense of happiness is derived from stability of mind.
The stability of mind comes from the state of one-no anxiety, no irritability and no anger.
Human's mind is controlled by neurotransmitters,like serotonin, dopamine,and noradrenalin.
Serotonin is the most important hormone of happiness-sense.
When this hormone is insufficient, human suffers from anxiety,irritability,
anger,depression and panic state.

Serotonin is secreted from brain, and cannot be acquired from external route,like ingestion.
It is affected by day-light,walks,carbohydrate ingestion.
Adequate outdoor sports is very important for the serotonin supply.
When serotonin is insufficient,melatonin also lacks and sleepdisorder(insomnia) develops.
And serotonin also control appetite. If it is lacking, obesty comes with. Anti-obesty drug,
Reductil(Sibutramin),contains serotonin.

Antidepressive drug is acting against serotonin reabsorption.

The sense of happiness comes from sufficient serotonin secretion.
Tranquilization of mind is the essense of happiness.
When we are happy,we donot feel anxiety,stress,fear,anger and restlessness.
And we sleep well and diet-control is also within our power.

These happy sensations derived from Serotonin.
And serotonin is well secreted when we do regular outdoor walks and intake adequate material .

Sufficient serotonin secures us mental concentration.
Good scholastic performance comes from adequate serotonin supply.

If we donot feel happy, we should make doubt of serotonin insufficiency.
And we should make haste to supply adequate serotonin.

Serotonin is made from essental aminoacid triptophan.

If we can supply serotonin externally, happiness is also buyable.