system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How/why are we able to physically feel emotions?

This morning I was laying next to my boyfriend and I found myself missing him. Physically, my chest felt tight and buzzy.  I remember in high school physically feeling my heart break after break ups. Or the butterfly in your stomach feeling.  How and why does this happen?
gpt
It has been proven that the brain perceives emotional pain in a similar way to physical pain.
Missing someone causes stress and worry to which brain answers with the physical response of muscle tightness, increased heart rate and shortness of breath. 

A heartbreak results into insane amounts of stress which activate the fight-or-flight response where the heart starts pumping more blood, muscles clench and you start breathing faster because you feel in danger and as though you have been hurt.
The brain is also taken aback by the emotional shock and is trying to take control of the situation, but it is stuck in a period of analysing and processing the shocking situation.

Butterflies in the stomach are caused by a reduction of blood flow to the organ as a result to anxiety or excitement. The adrenaline is released to increase the blood flow and rush more blood to the muscles to get you prepared for flight or fight.

We feel these intense feelings in response to our emotions in order to adapt to situations and prevent making the same mistake. You feel the heartbreak because the partner your brain and body has accepted as a potential mate has rejected you after you formed an emotional attachment.