(1) Satan was/is cherubim I don’t know whether or not they are flesh and blood or if they can “take on” other forms. My gut feeling is that evil is more spirit than substance.
(2) Depression has at least some base in chemistry, so I can’t say for a fact that is what I mean by being consumed.
(3) I need to say that I am in no way a Biblical scholar, theologian or even on the right path in life. I hold rather unusual beliefs, probably unique is a better word. In fact I know more about what I don’t believe than what I believe in.
(1) Biblically speaking, Satan is Lucifer who was an angel. There is evidence in the Bible to show that angels have the ability to be seen by man.
(2) I would agree that "chemical imbalances" are not possession, but rather a result of sin.
(3) Stick around on this thread and we can find out how are beliefs are the same and/or different.
I expect two or three others to join the discussion in the near future.