Terminal lucidity as well as activity may happen when the brain/body realizes it is really losing it, and mounting any and all last reserves of energy, instead

Terminal lucidity as well as activity may happen when the brain/body realizes it is really losing it, and mounting any and all last reserves of energy, instead of conserving energy for a long healing process. So it's consistent with compromised physiology, when activation can overcome whatever is otherwise stupefying or immobilizing. Something similar happens in some recoveries which then fade. People will come out of a coma briefly and seem fine, and then go back, never to return. Very difficult to study. Also this is quite distinct from what you might have meant: for elderly who have accepted their death, they may experience peace with anything in their experience.