Firstly, the cause of depression could be negative thinking like Basic diseases of brain: being selfish, you think superior to others and try to have fun with that, or hate someone, yet you like being in his company, jealousy, greed.
Actually it could be anything related to these thoughts which when you have brooded upon, find it negative. You might feel insecure if you try to get rid of them. Its for your good to get rid of them as soon as possible.
So, you need to check these thoughts and kill them completely and thereby stop this further production of 'black cloud'. (Actually you are right about it. Some people get it around the chest which even 'darkens' your vision. my cousin sister has been suffering from depression, suicidal tendencies, excessive attachment, guilt etc since childhood. Through my observation I have discovered (beyond doubt) that she is arrogantly selfish and it is a kind of permanent thought process that one get out of spontaneous learning(in experience). I have told her to stop being selfish but she didn't take it and denied it.)
I am mentioning an exercise which will not vanish this black cloud (for that take appropriate psychotropic medicine) but it will give you strength.
Sit on a chair with spine straight, chest out, shoulders pulled back. Breathe in through your nose slowly and deeply into your chest, hold the in-breath AND AT THE SAME TIME TRY TO INHALE MORE AND MORE AIR INTO YOUR LUNGS through your nose so that you feel a pressure or a strain, hold this position for as long as you can, now slowly breathe out through the
MOUTH.
Repeat this exercise as many times as you could. 5-10 times a day. No nutrition required to make this exercise efficacious.
Also listen to your inner self which means that does it try to stop you from doing, speaking or thinking of something. If you find something of that sort, follow it and also write it down somewhere.
For example, i was reading a poll in which someone asked whether he can allow his spouse to have sex with another person and enjoy seeing that. To this 89% of people said no. Its a naturally positive response that these people do have a connection with their inner self. It is not their thinking that stops them from such an act, it is their inner self, a product of nature that stops them from doing it.