I am going to make this post short, sweet and effectively to the point.
It is not true that if a person has true faith that they can not feel depressed or cannot experience bouts of depression and sadness. It is not true that a person who suffers from depressive or anxiety type illnesses is essentially suffering from low Imaan.
The Quran itself is filled with stories of great sadness and hardship. The Prophet SAWS experienced his own great sadness and a Year was in fact known as Ām al-Ḥuzn, the Year of Sadness in which his beloved Khadiga RA passed away and his uncle Abu Talib died. The prophet also stopped receiving revelation from Jibrail for a period of over 6 months in which he felt an enormous depression. Ya’qub (AS) cried until he became blind from the great sadness he felt when he lost Yusuf (AS). Let me reiterate again, that depression is NOT a lacking of faith.
Suffering from sadness or depression does not make you weak, it doesn’t come from you not being grateful enough or even religious enough! Depression is not your fault. Depression does not mean you don’t have enough faith or that God is angry with you or has forgotten you.
We need to remember that Allah tests different people in different forms, and by His help every single test can become a tool to get closer to Him. Remember “Verily, with hardship their is ease.”
Depression is NOT a lack of faith.
This too shall pass.
Serotonin Syndrome 