Symbolism, Imagery, Allegory
James equates addiction and despair with cold and darkness. (How original.) Recovery is a dark process, as we see when James says early on, "I am an Alcoholic and I am a Drug Addict and I am a Criminal. There is no light at the end of the tunnel" (1.7.376).
He is "cold" and "shaking" (2.1.1) when he sits outside experiencing withdrawal hallucinations—although we think anyone sitting outside in the woods in Minnesota around wintertime would be cold. But James does use the weather as a reflection of his inner turmoil: "It is still black, still storming" (1.8.3) during and after the dental procedure. Then, when James storms outside in in a suicidal huff and gets into a fight with Leonard (who is trying to save his life), we find out that "the cold is quick and bitter" (1.8.318), just like James.
You get the idea. In this book, dark and cold = bad. Real bad.