I dislike the term "disturbed" because it seems to imply that we know what "normal" is, and I don't think one can know that. If what you mean is "inscrutable," you have a case.
1. What is his motivation for treating Othello in such a horrific way? The play never explains. It is unclear that he gets anything out of bringing Othello down. While the motivations of most people are over-determined (that is, proceed from a number of different causes), Iago's seem _un_determined.
2. He is quite willing to use his wife cruelly in the above scheme—not seeing what it will mean to her when or if the dastardly plan unravels.
3. He is a sinkhole of contradictions, both affirming and denying himself at the same time, himself and a person apart from himself. As he says early on to Roderigo:
I follow him to serve my turn upon him [Othello],
We cannot all be masters, nor all masters
Cannot be truly follow'd. You shall mark
Many a duteous and knee-crooking knave,
That, doting on his own obsequious bondage,
Wears out his time, much like his master's as s,
For nought but provender, and when he's old, cashier'd:
Whip me such honest knaves. Others there are
Who, trimm'd in forms and visages of duty,
Keep yet their hearts attending on themselves,
And, throwing but shows of service on their lords,
Do well thrive by them and when they have lined their coats
Do themselves homage: these fellows have some soul;
And such a one do I profess myself. For, sir,
It is as sure as you are Roderigo,
Were I the Moor, I would not be Iago:
In following him, I follow but myself;
Heaven is my judge, not I for love and duty,
But seeming so, for my peculiar end:
For when my outward action doth demonstrate
The native act and figure of my heart
In compliment extern, 'tis not long after
But I will wear my heart upon my sleeve
For daws to peck at: I am not what I am.
The above has the air of being a confession, yet what Iago confesses he...