Yes, he had some kind of hereditary disease which inhibits his body's blood-clotting ability. Thus, his caretakes must be extra careful.
The day he died, he had fever. The doctor was supposed to use acupuncture to save his life, but then the doctor decided NOT to do that... Therefore, 五阿哥係因為御醫刻意不搶救而死。
Actually, I find this show hard to understand... 對白懶深,講到唔清唔楚,睇咗十幾集先至適應...