@Mame,
Somewhat before I had to put down my dog - no, I am in no way equating that with having my/a sister dying, trust me - I mentioned on a2k that I tended to cry in the car. A poster suggested it was a sign of serious depression and, if I remember, that I should connect to a counsellor. But I'd been through grief before, and recognized it.
I also recognize your comment on 'welcome the pain'.