the crucial thing forgotten
He had the nightmarish feeling that there was something crucial he had to do but had forgot what it was. 10-mg. injections of the Blue Bayou kept the feeling at bay for shorter and shorter periods.
Context
Conscience surviving the anesthesia as a nameless dread: buried under the binge is the knowledge that a man is dying in the corner and that Gately is supposed to help, and it surfaces only as a formless nag that there is "something crucial" undone. And the addict's answer to conscience is the same as his answer to everything — another injection to push the feeling back down — except the intervals of relief keep shrinking, the dose losing the race against the thing it's trying to blot out. The moral faculty isn't gone; it's just outbid, shot by shot.