In the Name of Allah, Most Merciful and Compassionate
All praise to Allah, Lord of the Worlds. And salutations and greetings upon our Master Muhammad and upon his family and companions.
It is very recommended to send a lot of blessings upon the Beloved of Allah, the Prophet Muhammad (Allah bless him and give him peace), for he is the ultimate mercy from Allah to humanity, and we have been informed, “Whoever sends blessings upon me once, Allah blesses them ten times .” This is explained to be the least of the reward.
The scholars mention that for those sick or troubled (and others) it is good to recite the Salat al-Tibbiyya, along with the sunna ways of sending blessings and peace:
Allahumma Salli `ala Sayyidina Muhammadin
Tibbil qulubi wa dawaa’iha
Wa nuril absari wa diya’iha
Wa `afiyatil abdaani wa shifaa’iha
Wa `ala Aalihi wa Sahbihi wa Sallim.
O Lord! Send blessings on our master Muhammad,
The medicine of hearts and their cure,
The light of eyes and their illumination,
The health of bodies and their healing,
And upon his family, companions, and send peace.
Taken from: http://seekersguidance.org/ans-blog/2009/08/11/lately-ive-been-feeling-really-down-depressed-can-you-post-some-duas-or-adhakar-that-might-help-with-this/