It's like a chill that creeps up your spine and raises your hairs on end. One of those emotions that does not shy from physical expression. A feeling that penetrates the body's very reflex engine. A multitude of tiny lightening bolts through your nerve endings that leaves your fingers cold and stiff.
Not that it's an entirely negative experience, though we certainly associate it that way. "Someone just stepped over my grave," many recite at such a moment. Facing mortality is also facing eternity. All of that to say, I've had those chills all day.