I have/had? major depressive disorder and OCD. In the past month, through excessive prayer, sacrifice of certain material items, ceasing willful sinning, and reading my bible, my symptoms have improved drastically and rapidly. None of the drugs I was prescribed before had this noticeable of an effect. I have also mentioned the religious nature of my OCD in a few other threads on here. That has all but left me this last week.
This is a very personal experience for me. The changes in me have been drastic. And the experience has been very real and life changing for me. I also have some strange sleep disturbances that have stopped completely. Take it for what you will.
I am not an advocate of all psychological disorders are caused by demons. I have theories on how demons attack. They can create, complicate, or have nothing to do with psychological disorders. They can implant thoughts that masquerade as our own, alter emotional states, create unnatural impulses, and attack physical health.
This is not to say that someone who develops a heart condition at a young age is necessarily under demonic attack, but it's very possible. This is not to say that everyone with a psychological disorder is under an attack, but it's very possibly that they are, and that the symptoms could be worsened by attack. Or it may not be demonic at all.
I think too many Christians deny the fact that demonic entities do in fact work in the world. You can't do this. How can you believe in a God, who came into the flesh, died, and resurrected, but you can't believe that demons may in fact have something to do with what is happening to us? You say that Satan tempts you. How!? He's not there in the flesh in front of you tempting you is he? Could it not be that thoughts of sinning are implanted, or impulses to react to certain outside stimuli are in fact not from you? Wouldn't true temptation make more sense this way?
But you can't leave the nature of our sinful flesh. We are as much responsible for stuff through our own choices, but I don't believe it is all from us. Ultimately it is our own fault, but that's not to say we can't be coaxed into sinning, or that we cannot be attacked.
If you say satan is tempting you through other people, how is he doing it!? Couldn't it be that they are giving into impulses or compulsions to try and get you to sin with them? Think people. They do operate on a level we don't see. But I think its possible to spot their activities. But, like in another thread that was up, you can't blame -everything- on demonic activity. What you can do, is at least be aware of the possibility.
Just my thoughts on it though, and purely opinion.