As a result of Hamlet's prolonged act of being mad, he does indeed become mad himself. As we know King Claudius murdered Hamlet Sr. Upon hearing the news of the true actions taken, Hamlet sets out to avenge his fathers murder. With all of his anger he is viewed as being mad by society, King and Queen and his peers, Right? Okay so what makes him mad? Let's see, the definition of insanity is, it's a condition in which a person is utterly senseless; and irrational, by reason. So as we see Hamlet acted out of pure passion and insanity during his quest for revenge.
We first see Hamlet going completely off the deep end into the ocean when he encounters Ophelia for the first time after he makes his revenge well we see that he used to treat her with respect and kindness, to treating her like a piece of crap he just stepped in and wiped off onto the sidewalk. This is completely senseless and irrational on his part. In the first part of the play he writes in a letter to Ophelia "Doubt thou the stars are fire, doubt that the sun doth move, doubt truth to be a liar, but never doubt I love" These words sound sweet, and romantic right? Well why the sudden change of heart? Only a few days later Hamlet denounces his love, and accuses her of being dishonest, saying "I did love you once. I love you not. if thou dost marry, I"ll give thee this plague for thy dowry: Be thou as chaste as ice, as pure as snow, thou shalt not escape Calumny." (133).
Also making him seem a bit. hmm. Shady you could say, is his constant struggle with how to react to his fathers call for revenge. He's just being stunned and can't decide "whether tis nobler in the mind to suffer the slings and arrows of outrageous fortune, or to take arms against the sea of troubles and, by opposing , end them. (127).
Another thing making him. well let's see. Wacko is in Act four, scene two when he is talking to Rosencratz and Guildenstern about the murder of Polonius and where he put the body.