Definition of "sleepwalker"

Edward Churchill still attended to his work in a hopeless mechanical manner like a sleep-walker who walks safely on a well-known round. But his Roman collar galled him, his cossack stifled him, his biretta was as uncomfortable as a merry-andrew's cap and bells.

1918, W[illiam] B[abington] Maxwell, chapter XV, in The Mirror and the Lamp, Indianapolis, Ind.: The Bobbs-Merrill Company