Everyone carries around him an environmental consciousness or atmosphere through which he is in relation with others or with the universal forces. It is through this that these forces or the thoughts or feelings of others enter.
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Each man has his own personal consciousness entrenched in his body and gets into touch with his surroundings only through his body and senses and the mind using the senses.
Yet all the time the universal forces are pouring into him without his knowing it. He is aware only of thoughts, feelings etc. that rise to the surface and these he takes for his own. Really they come from outside in mind waves, vital waves, waves of feeling and sensation etc. which take particular forms in him and rise to the surface after they have got inside.
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But they do not get into his body at once. He carries about with him an environmental consciousness (called by the Theosophists the aura) into which they first enter. If you can become conscious of this environmental self of yours, then you can catch the thought, passion, suggestion or force of illness, or whatever it may be, before it enters and prevent it from entering into you. If things in you are thrown out, they often do not go altogether but take refuge in this environmental atmosphere and from there try to get in again or they go to a distance outside but linger on the outskirts or even perhaps far off, waiting till they get an opportunity to attempt entrance.
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These [forces of depression, dullness of mind, etc.] are things that wander about in the atmosphere and jump upon one without notice. It is often difficult to see where precisely they come from and often there is no reason at all or any inviting cause in oneself. They have simply to be thrown off as when something falls on the body.
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The Parts of the Being and the Planes of Consciousness, Letters on Yoga- I, CWSA, Sri Aurobindo.