What emotion are we talking about here?
Caffeine is a stimulant. This can cause your nervous system to become hyper-aware; which in turn can cause an increase in your stress level. Caffeine causes a rise in both respiration and cardiac function. The hormone adrenaline is secreted by the adrenal glands in response to stimulation of the sympathetic nervous system. It causes what is known as the "fight-or-flight" response.
Answer: When people become addicted to any form of drug you'll often spot mood swings and mental health issues. Fidgeting is common amongst some.
