Carl Lange and william james developed a theory of emotions whereby emotions are the result of bodily reactions rather than the reverse.
According to James-Lange theory, external stimuli in the environment are received and decoded by the brain, but even before you consciously process it, your body is already responding with physiological changes such as increased heart rate, altered blood pressure or even pupillary contractions / expansions. So the emotions you develop are really based on these physiological changes. In other words, you might ask something like, “Why am I feeling excited?” James-Lange's explanation would be that, as you are breathing fast and your heart is racing faster, your brain concludes that you are excited!
