A cerebral aneurysm consists of "a weakness in a blood vessel in the brain that balloons and fills with blood." Reports claim that Jung Il Woo suffered from headaches and migraines over the past 3 years, and the primary cause of his diagnosis is most likely his car accident back in 2006. Jung Il Woo was with fellow actor Lee Min Ho at the time, and both suffered from severe injuries.
If aneurysms in the brain rupture due to stress caused by strong emotions or from high blood pressure, it may cause life-threatening bleeding. The only way to completely treat an aneurysm is through surgery, and supposedly, Jung Il Woo has been going through regular examinations, watching his symptoms carefully.
Despite the likelihood that if he goes through a re-examination, he may receive an exemption from his mandatory military service, Jung Il Woo will reportedly choose to carry out his active duties. He'll receive training as formerly announced next month before being assigned as a social worker for 2 years.