DEMETRIUS: For I am sick when I do look on thee.
HELENA: And I am sick when I look not on you.

– William Shakespeare

A Midsummer Night’s Dream, Act 2, Scene 1. In a bid to convince Helena to stop chasing him, Demetrius insults her by saying that he is literally sick at the sight of her. Poor Helena, obsessed with Demetrius and desperate for his love, replies that she feels ill when she doesn’t get to see him.