Grief and unhappiness will effect your immunity, at the very least. When my uncle passed away from cancer last July, my aunt was erratic with her medication and her immunity was suppressed (she lost sleep, ate inconsistently, and was very unhappy), and it was a major playing in causing her own cancer to return.
When I heard about it’s return and the hit to her health, I was so upset and distraught at the news that I lost sleep, and the cold virus that was on it’s way out returned in full force and stuck around with me for an extra week.
The mind and the body are one, and what we think and what we feel has direct impact on our health.