Many of those who have mental disorders were excessively happy childs and when they fall in mental prison, the journey of torture starts, some people suffer from Social anxiety first, then after few years and as result of Social anxiety, they fall in deep depression and some even suffer from OCD after suffering from those both mental prisons.

Causes

Scientists say that Serotonin level in depressed people brains is less that of Happy people

Genetic causes

Solutions

Some use medications which sometimes help and sometimes make situations worse with exhausting side effects

Some use Cogntive Behaviour Therapy which can help in the long term but many but it is not effective so much, it only decreases exhaustion, depression and stress but it doesn't make you happy, it is possible that some got away from mental prisons by CBT but I think most still have chains on their body.

For Social anxiety

Postive self talk works in the long term
Gradual exposure to delusional fears works in the long term if done continously
nurturing self esteem helps a lot

For Depression

Excerise helps a lot
Going out
Travelling
Learning something you like to keep your mind busy and off yourself.
being postive and optimistic
venting
discipling yourself

It is better to improve the mental condition, maybe improvement after improvement can lead to the biggest improvement.

Thanks