Act IV is full of imagery of diseases and illnesses. Here are some examples:
Mad as the sea and wind when both contend
Which is the mightier. In his lawless fit,
Behind the arras hearing something stir,
Whips out his rapier, cries 'A rat, a rat!'(10)
And in this brainish apprehension kills
The unseen good old man.
This is Gertrude speaking to Claudius about Hamlet in Act IV Scene i. The first word "Mad" must be taken literally (meaning insanity), for Getrude is now convinced that Hamlet suffers from some form of madness. The word in line 8, "fit", however, is not to be taken literally but metaphorically, for Hamlet was not having an actual epileptic "fit" or seizure, but instead, Gertrude is saying, Hamlet is overtaken by a "fit" of (possibly temporary) insanity. Claudius responds:
Alas, how shall this bloody deed be answer'd?
It will be laid to us, whose providence
Should have kept short, restrain'd, and out of haunt
This mad young man. But so much was our love(20)
We would not understand what...
(The entire section contains 581 words.)