Whether one is elated or depressed it affects them physically.
During the "infatuation phase" of a new relationship it's not uncommon to be able to work all day, go to the gym, come home and shower, then go out to dinner, dancing, have sex all night, and get up early to start the next day. It's as though "new love" give us a physical energy boost. A couple years later into the relationship neither person is up for doing that much activity in one night. The excitment or high that use to be there along with the "excitement and anticipation" of seeing them fades.
Heartache is usually the result of "shock" that it's over.
You are caught off guard. Something you were once "sure of" has been pulled from underneath you. Your mind races and you wonder how could you have not seen it coming. You can't sleep. There's a little bit of an "identity crisis" especially if you have been known as part of a "couple". Depression can lead to not eating or over eating, not sleeping or refusing to get out of bed.
Our thoughts and emotions have a direct effect on our physical well being. Imagine getting fired from your job during the day and then winning the lottery that night. You'd go from depression to elation in the same 24 hour period based upon "words" you were told.