The lethargy must have his quiet course:
If not, he foams at mouth, and by and by
Breaks out to savage madness.
– William Shakespeare
Othello, Act 4, Scene 1. Iago says this to Cassio when Othello collapses in an epileptic fit after being overcome by jealousy. Cassio wants to rub Othello’s temples, but Iago tells him to leave Othello be, otherwise he will foam at the mouth and go completely mad.