the chainsaw head of the cold quit
It was as if his head perched on the bedpost all night now and in the terribly early A.M. when Hal’s eyes snapped open immediately said Glad You’re UP I’ve Been Wanting To TALK To You and then didn’t let up all day, having at him like a well-revved chain-saw all day until he could finally try to fall unconscious, crawling into the rack wretched to await more bad dreams.
Context
Withdrawal a week-plus in, rendered as a head that has become a separate hostile person: it greets him the instant his eyes open, saws at him all day, and hands him bad dreams the moment he escapes into sleep. What drives Hal toward the Program is not the craving — he hasn't touched a substance — but this, the round-the-clock wretchedness the abstinence itself has opened, the mind with nothing to medicate it turning on its owner.