As I understand it, Halloween was originally a sort of Celtic festival of the dead, and they thought that at this time, the barrier between this world and the next was easier to reach across than at other times. I'm about half Irish, and this past October 31st happened to be on a Monday. I think I've posted about the Monday Candle Ceremony that is done at various places around the world, but at 10PM Eastern time. Late October is at least somewhat close to either the anniversary or presumed birthdays of cats Tomkit (1956), Peasant (1963), Ambrose/Fluffy (1979- actually I started taking care of him around mid-summer, but I was thinking of him), Riley (late November 1994), and Crystal (September 2001); also Dory the hamster (late October 1996). So I celebrated their lives, and managed to keep it happy.
I neither saw or felt any ghosts, though (either human or animal); I never have, but often think I'd like to.