How does the author use foreshadowing in The Imaginary Invalid?

In Act I, Scene I, the main character, Argan, is adding up a large tally of bills from his apothecary, and he makes the comment out loud, to himself, that he is ill. He is also obviously taking many prescriptions. The example of foreshadowing is used to imply that the main character has many idiosyncrasies to reveal.