Atomic coffee adds a LOT of negative fatigue. Single bag of coffee powder (20) can be split into 100 units of coffee syrup, which then can be turned into 100 units of atomic coffee.
Each unit of atomic coffee gives you 300 units of negative fatigue.
Each unit of fatigue drains 1.5 points of heat. For comparison, each unit of clothing warmth gives about 45 points of warmth (actually 30 to 60 points, depending on how hot/cold are you at the moment).
This means that a single atomic coffee gives you about as much warmth as adding a 10 warmth clothing to entire body.
“Tired” is 191 fatigue, “Dead tired” is 383 fatigue, “Exhausted” is 575. Two atomic coffees are enough to make you fully awake from being exhausted.
This extra heat only happens in old stable. In new stable and in experimental you can only lose heat from being exhausted, never gain it. I think you still can be anti-exhausted and thus prevented from sleeping for few years if you overdose on coffee.