One who is depressed is NOT one whom is "insane."
People become depressed for myriad reasons. There is no "one" cause.
No one WANTS to be depressed.
One deals with depression by seeking professional help.
If you no longer enjoy life, even something as benign as texting a friend, you need help.
Should we "accept the chemistry of our brain......."
Since you are posting here, I'd say you've answered your own question.
The question of how high Western culture has "set it's bar" of fitness is a moot point.
If you are unhappy, then it is you, and ONLY you, who can judge what is "normal."
Only YOU can know if you're on the right.......or wrong.......path.