I noticed that my survivor was overheating regardless of clothing and weather, reaching scorching levels in the middle of a chilly night rain. At first I thought it’s just new temperature system being all wonky, but when I cheated in a power armor (it has THERMOMETER flag and thus shows accurate temperature), it showed mere 14 degrees (Celsius).
I checked src/player.cpp for bodytemp and noticed that non-sleeping survivors’ temperature is affected by tiredness. I checked my save: -3721 fatigue. So that’s where all that atomic coffee went.
Maybe there should be some sort of cap on negative fatigue? Excess could go to stimm or even cause some sort of a disease (tremors).
tl;dr Atomic coffee can turn your survivor into a walking (Godzilla-style) biological reactor who sweats superheated scalding steam in the frozen center of a winter lab.
Symptoms of Caffeine (Found in Coffee) Overdose include:
Breathing trouble
Changes in alertness
Confusion
Convulsions
Diarrhea
Dizziness
Fever
Hallucinations
Increased thirst
Increased urination
Irregular heartbeat
Muscle twitching
Rapid heartbeat
Sleeping trouble
Vomiting
Basically you’re over-stimmed and your heart is gonna go boom-boom. Enjoy. 
I once drank enough atomic coffee I didn’t sleep for 2 seasons. The neg fatigue explains it.
Scorching seems a bit much for fatigue…but this is nuclear coffee. I think it destroys any expectations I can have.
It seems like the real problem here is that the amount of heat you put out should cap at the “fully awake” point, not continue to increase as you get farther and farther from sleep. 
Thanks for reporting this, as a band-aid I’m going to cap the body temperature effect, longer-term we should have separate “fatigue” and “stimulant” effects that fight it out when this kind of thing happens, then the only thing that can actually lower fatigue is sleeping.
I was kind of wondering what had me turning into some sort of Attack on Titan steambeast.