If a person's head was cleanly and rapidly decapitated by a sharp blade slicing through the neck, such as would happen on the guillotine, could that person remain conscious? If so for how long? Long enough to be aware of (the head) falling down and hitting the ground?
Obviously it would be brief due to lack of blood supply, but it seems plausible that it could be a few seconds.
Or is there some inherent neurological shock due to the severing the top of the spinal cord that would cause near instantaneous loss of conciousness?
Could Marie Antoinette have seen her own severed neck from the basket below the blade?