The Hanahaki Disease.

An illness that suffocates it's subject to death by the blossoming of a flower within their chest cavity. This disease is born from one-sided love. Symptoms of it consist of coughing or even throwing up flower petals, as well as a throbbing pain within the chest that worsens along with the disease. There is no known medical cure for the disease, and it will continue to progress for as long as the subject suffers from the one sided love.

The only known cures for the disease are when the subjects feelings are returned, or their feelings for the other become nonexistent.

It didn't surprise Jimin when he started to cough up crimson red rose petals.