Caffeine accelerate the engine which crashes without fuel (carbs/glucose).
Caffeine + fasting = cortisol
Symptoms to expect when you do coffee right are calmness, focus, motivation, warmth, and stable energy. Coffee done wrong leads to anxiety, shakiness, sweating, feeling wired, inability to focus, and sometimes cold extremities.
No, it's more of a "metabolic engine crash".
Cold does the opposite tbh, it's most suited for people who have a strong metabolism. Fasting also makes things more difficult for people with metabolic issues because it triggers cortisol.
It sounds like caffeine is helping to kick-start your metabolism. Some people combine it with theanine which helps to block the negative cortisol effect that caffeine causes for some people.
I don't use caffeine.
Billions of people self-medicate with caffeine to support their metabolism. The people with an underactive metabolism tend to really enjoy caffeine and rely on it to function.
It sounds like you're relying on caffeines metabolic boosting effect. To paraphrase, "caffeine does what thyroid would normally do". People with thyroid (metabolic) issues love caffeine, especially those with hypothyroid (see image below).