I've had this twice. Once to a car accident on the motorway in 2002. Once to a bizarre form of leukaemia such that (from our perspective) the guy had back pain on Thursday, and died over the Easter weekend by Tuesday in 2009.

Still think of them both from time to time. Some of my now-ex colleagues still comment on the anniversary of their passing on Facebook. I don't think I could honestly remember the dates if they didn't... Their names always stick with me though.