Lear explains what happened with Goneril to Kent (who is still disguised as Cauis), and then sends Kent to deliver a letter to Regan. Assuring Lear that he will not sleep until he has delivered the message, Kent speeds off.
Kent continues to show exemplary loyalty to Lear (though he has to maintain the disguise of Caius in order to do so).
As he prepares to head for Regan's castle himself, Lear is teased by his Fool, who predicts that Regan will be as like Goneril as "a crab […] to a crab" (1.5.18). Meanwhile, Lear begins to rave, fearing that he will go mad at the "monster ingratitude" (1.5.39) that Goneril has shown him. As the Fool persists telling Lear "thou wouldst make a good Fool" (1.5.38), Lear begs: "Sweet heaven!/ Keep me in temper. I would not be mad!" (1.5.46).
The Fool also continues with the kinds of animal metaphors that Lear introduced in his curse of Goneril. Lear, meanwhile, having realizing that in giving up power he has lost his identity as king, calls out to the even higher power of heaven to help him, as he fears that in losing his identity he may fall into the chaos of madness.