I remember once hearing from a priest despair was a sin. It was difficult for me to wrap my mind around this. Because I feel empathy for people who are in despair, However I can see it is a lack of faith to be in despair. However, it is possible other worldly things, could actually be the cause of such a thing, feeding off our negative energy. This I believe Jesus recognized, and cast out demons, which is like the parasite. I see him as casting out parasites out of people, who had lost their way. Other folks thought the people deserved the demon possession because of sin. He didnt care, and didnt see purpose in this, so he cast them out, anytime he would encounter one with demons.
The parasite tries to put you in despair and have you lack faith in yourself, and in Spirit. And feeds off your fear, your despair, your anguish, but all in all, the negativity you exude in the process. It wants you to lose your way and be in a hopeless state, because when you are in this state you lose your connection with Spirit. Spirit is full of love and understanding, and is ready to take up house within our souls. But to really truly, have the Spirit enter us, so we may get on the path, we have to get clear of the parasite. And one of the main ways is to begin to have faith. If it is difficult to have faith in yourself, begin by having faith in Spirit, that all things are possible. Understand that you are worthy and loved beyond comprehension. And then continually talk to Spirit all the time, for aid, for communion. From this, the more you absorb yourself into the Spiritual, then the Spirit can take up residence in your being and your life. But you have to fight the negative and like Michael said, realize it is not you. To get so angry, to get so sad, to get so wrapped up in the negative, the parasite wants. To have faith, to be loving, to be good basically, it does not want. Keep fighting when the thoughts arise. Recognize they are not you. Recognize the good in your life and embrace it.
This is the source of additions. This is an affliction - but it involves submission of the individual. Don't submit!