A human's own mind becomes his/her own enemy if it is not maintained in a proper way.
Human beings are ruled by spirits but humans must learn to control and rule the spirits. Spirits possess people according to the mental state of the human beings and keep them in the same state until they are rejected and replaced by another. This is an all time phenomena occurring in all humans. Human beings are always under the influence of spirits. Certain situations and circumstances causes the possession of certain type of spirits. Often thinking and talking about bad subjects or bad imaginations even for fun can take serious turns on one who think and talk. All spirits (good and bad) have the dominating character. They can take you to the extent of sacrifice or suicide.
All of your activities, talks and even thoughts determine what kind of spirits you will have for your life. Only these spirits are the reason for the good and bad happening in your life. Generally spirits determine your destiny from your daily activities, talks and thoughts too. All knowledge, skills, emotions, feelings, interests and everything are spirits. Even thoughts are not your own. For example, when you want to take a decision on a subject, one after another they think and you just listen and choose or reject the ideas which they transmit to your mind through your brain in the form of thoughts. A human being during his/her lifetime is living with many spirits which have joined one by one since birth. All human beings are just unprogrammed robots made of flesh, bones, tissues etc., by birth and toys of the spirits for their games.
You must not leave your mind in it's own way. If you do, the spirit will take your mind for it's own, then controlling it is not so easy. First of all you must think and believe that it's not you. Then you must command that spirit both mentally and orally to go. Whenever you are possessed by that thought you must divert your mind at once towards some other subject and stay in it for a while and then continue your duty. This is a mental exercise. You may also bring at once an opposite feeling through your imagination. For example if the depression is about your future then you may think, imagine and believe that you are going to live a healthy, wealthy and happy life in future. You must continue this exercise for few days. While doing this exercise you are creating an opposing spirit, i.e., a positive force. Soon this new spirit gets stronger and eliminates the negative force. Within a few days you will be alright.
Remember! Only your positive thoughts can get you out of your negative feelings.