The cancer he had when he was younger was a type of lung cancer.

His symptoms were:

. Cough that is not cured even after a couple of weeks
. Wheezing, hoarseness of voice, or chest pain
. Fever
. Shortness of breath specially on exertion
. Blood in cough
. Tiredness and weight loss
. Recurrence of infections
. Swelling of neck or face

Thankfully, he is cured from his cancer now. However, he still has trauma that he deals with, and quite a lot of other things that he deals with.

More Of His Conditions:

Depression

Signs & Symptoms
Emotional Changes:
. Feelings of sadness, which can include spells of crying for no apparent reason
. Frustration or feelings of anger, even over small matters
. Feeling hopeless or empty
. Irritable or annoyed mood
. Loss of interest or pleasure in usual activities
. Loss of interest in, or conflict with, family and friends
. Low self-esteem
. Feelings of worthlessness or guilt
. Fixation on past failures or exaggerated self-blame or self-criticism
. Extreme sensitivity to rejection or failure and the need for excessive reassurance
. Trouble thinking, concentrating, making decisions, and remembering things
. Ongoing sense that life and the future are grim and bleak
. Frequent thoughts of death, dying, and suicide
Behavioral Changes:
. Tiredness and loss of energy
. Insomnia or sleeping too much
. Changes in appetite- decreased appetite and weight loss, or increased cravings for food and weight gain
. Use of alcohol or drugs
. Agitation or restlessness- for example, pacing, hand-wringing, or an inability to sit still
. Slowed thinking, speaking, or body movements
. Frequent complaints of unexplained body aches and headaches, which may include frequent visits to the school nurse
. Social isolation
. Poor school performance or frequent absences from school
. Less attention to personal hygiene or appearance
. Angry outbursts, disruptive or risky behavior, or other acting-out behaviors
. Self-harm- for example, cutting, burning, or excessive piercing or tattooing
. Making a suicide plan or a suicide attempt

Jaehyun also deals with a slight form of Anxiety.