I'm sure people do, however if I had to take a guess id wager that it's the headspace someone's in during their suicide. For them to laugh, I'd feel they have to be incredibly unstable atm of death, which for some, especially those who take hypoxic methods, there would be more stable, and calm mindset, as they push towards peace.
Then again idk. For me, if anxiety hit I'd probably laugh, since it's almost a reactive mechanism when I'm freaked out.