I think for hamlet, it's mostly madness that has consumed him. He seems to be on the edge of both sanity and madness sometimes, making good and bad choices. But the way he killed Polonius instead of the king by “accident” indicates something of madness. And the fact that he didn't really care that he killed Polonius, as if life doesn't matter, makes it seem more sensible to believe he's not sensible. The way he treats Ophelia too, says something about whether he's not right in the head. Toying with her and her emotions like how he did, it was partially messed up. Lastly, there's his revenge plan he's working towards, to avenge his Father. He couldn't talk about it sensibly like a normal person, revenge is the only way
