past the crest into the cold
A disadvantage of your nasally ingested cocaine being that at a certain point somewhere past the euphoric crest—if you haven’t got the sense left to stop and just ride the crest, and instead keep going, nasally—it takes you into regions of almost interstellar cold and nasal numbness. Randy Lenz’s sinuses were frozen against his skull, numb and hung with crystal frost. His legs felt like they ended at the knees.
Context
Relapse phenomenology delivered as a clinical-comic weather report: past the point where a person with any sense left would stop and ride the high, the drug stops warming and starts freezing — interstellar cold, numb sinuses, legs that end at the knee. The pleasure has inverted into anesthesia, and the anesthesia is the reason he cannot feel that he should stop.