:salam2:
Depression has been vigorously studied and there is different solutions to varying age and/or circumstances.
It would not be fair to suggest a remedy to one person who is 19 versus an older 40 year old.
The 40 year old may be acquainted with more people whom may have passed away and is noticing it more. While a 19 year old maybe uncertain on what to do as a focused career.
Longer periods of depression need the attention of medical professional, as I could recall like greater than 2 weeks straight.
In the Quran Allah mentions in surah Azzumar 39:53:
Say, "O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful."
Then on:
[Saheeh_International] And when We let the people taste mercy, they rejoice therein, but if evil afflicts them for what their hands have put forth, immediately they despair. [30:36]
Then:
[Saheeh_International]
And if Allah had extended [excessively] provision for His servants, they would have committed tyranny throughout the earth. But He sends [it] down in an amount which He wills. Indeed He is, of His servants, Acquainted and Seeing. [42:54]
And it is He who sends down the rain after they had despaired and spreads His mercy. And He is the Protector, the Praiseworthy. [42:53]
See buy doing good obeying Allah and understanding that trials are just like a test then understand and implement what prophet Ayub rahmat Allah alay did when he was afflicted with trials.
We don't have complete control to our circumstances but definitely have control of the effort of ibadah/worship. So when faced with challenges that arise to a point of depression it is best to increase the good deeds and be very patient. Just like the cloudy and dark full day passes and the next day the sun is bright and shiny and lifts the mood then finally we come to reality to Allah subhanna wata3alla to eternally light our way.
Depression is mistakenly identified with decrease in motivation or energy in mid adults. It is not depression but rather the growth hormones have diminished substantially. The area of the body that is responsible for this is just above the kidneys. As we get older our body produces less and less after adolescence which is normal. Sometimes the levels get too low and a little cost and harm supplement may recharge it. Try brown seaweed extract supplement 500mg/day.
Lastly remember to smile as this is the Qadah and Qadar of Allah.