Long-term stress erodes memory
By the far, the most stressful thing I've ever done is stay with my dad while he died of cancer. For the last two weeks of his life, I stayed at the long-term care facility he was at. I put all my client's projects on hold so I could be with him. I stayed perhaps 18 or more hours of each day. I slept in the chair next to his bed. I did my best to take care of what he needed. When he was in pain I would go out into the hall and plead with the nurses to get more pain medication, though sometimes they were hesitant because he had taken too much (long story there, and I knew nothing about how the system worked then, but apparently you have to say very specific words, which are full of legal meaning, to make clear that a person wants an unlimited supply of pain killers during their final days). When he was lucid we would talk. When he wasn't lucid, I would do what I could to comfort him. I was alone with him in the room when he died.<p>And after that... my concentration was gone. For a good two years. My ability to write code for 70 hours a week, and think of it as fun, was gone. My mental clarity was gone. It took a solid two years to come back, maybe three years.<p>My dad was my best friend and losing him hit me very hard. 
And I learned there are some kinds of emotional stress that take years to recover from.