GR translation: white overhead

[Mike Jing]

V61.13-17, P62.30-34   These changes on the text “You never did the Kenosha
Kid” are occupying Slothrop’s awareness as the doctor leans in out of the
white overhead to wake him and begin the session. The needle slips without
pain into the vein just outboard of the hollow in the crook of his elbow:
10% Sodium Amytal, one cc at a time, as needed.

What exactly is the "white overhead" here? Is it an overhead lamp?