For me it was my dad's death. Not the fact that he died itself (he was 95 and suffering severe dementia - it was definitely his time) but the nature of it.
After several traumatic hospital admissions for an infection he could not recover from we made the choice, with the approval of HCPs, to withdraw all forms of care apart from palliative, and to let him die at home.
As he was no longer eating or drinking I imagined it would be pretty quick. It lasted about 10 days. Watching someone you love die slowly in front of you like that is almost unbearable.
I was very close to my father, especially towards the end - after my mom I was his main carer, and because my mom is elderly herself (though heroic!) it was me who ended up sleeping the night on the floor of A and E etc etc towards the end. So it was me he generally wanted when he was most distressed/confused.
But on the last morning, my presence did nothing to calm him - nor did the dose of morphine and valium he had been given (we had to phone up and ask when we wanted him to get pain relief - it was injection only. And then it could take up to two hours for someone to come).
Lying on the bed with him and watching him writhe in pain and being unable to do anything to help him, was by far the worst experience of my life.
In the end, we managed to beg the district nurse to send someone, a lovely guy who agreed that dad needed more medication, and gave him a much larger dose of both morphine and valium, which helped him to finally slip away calmly that afternoon, with me, my mom and brother all in the room with him, holding him/his hand and telling him we would be ok and that it was ok for him to go.
A beautiful death, in the end, if any death can be said to be beautiful. But what led up to it, I found frankly unbearable.
It's had a positive impact on my life in a way though - I have stopped giving a shit about minor troubles/annoyances. And I have realised I am stronger than I thought - if you had asked me before, I would have said there is no way I could have stayed with him through that.