Bipolar, manic depression, whatever you wish to call it - is a genetic trait. So, the tendency to have this is scientifically identifiable through gene mapping.
I carry the gene, however only the women in my family develop the condition and with medication can lead quite normal lives. However, usage of steroids and high levels of stress can cause symptoms of this to appear even in the males of my family. And why, I am pretty sure I will not have any biological children, adoption is always viable.
With that being said, I too have wondered at the demonic ability to replicate this disorder or to have an "easy in" with those whom have this genetic trait.
So, I decided to study this from the perspective of: demonic demonstration/traits found in the Bible versus bipolar signs amongst the female members of my family. My conclusion is no, demonic possession or control does not equal real bipolar traits.
Conversely, those with bipolarism, do seem to be more likely to demonstrate what is over and above pure bipolar, and yes, even to the extent of demonic activity. In my research, Christian authors also pursued this same track of thought and came to basically the same conclusion.
So, I guess if it looks like a duck, smells like a duck and quacks, well with intervention the subject could be freed of the demonic activity but still will need medication to overcome the bipolar traits.
However, it is important to remember that the bipolar brain does not work the same as the average brain. What is perceived as a threat to the bipolar, will be viewed as perfectly normal by the average. So the bipolar brain will react to the threat perceived as if it is real and then appear to be completely whacked to anyone else. Logic has nothing to do with calming them back down or being able to see "correctly" that there was no threat. And why medication is needed to conquer the highs and lows of their perception.