The question is rhetorical. I know the answer only too well.
It is to count off and dread in the small hours the fateful harsh strokes of the chime. It is attempting with ineffectual magic to breathe smoothly. It is the burden of a body that abruptly shifts sides. It is shutting the eyelids down tight. It is a state like fever and is assuredly not watchfulness. It is saying over bits of paragraphs read years and years before. It is knowing how guilty you are to be lying awake when others are asleep. It is trying to sink into slumber and being unable to sink into slumber. It is the horror of being and going on being. It is the dubious daybreak.
What is longevity? It is the horror of existing in a human body whose faculties are in decline. It is insomnia measured by decades and not by metal hands. It is carrying the weight of seas and pyramids, of ancient libraries and dynasties, of the dawns that Adam saw. It is being well aware that I am bound to my flesh, to a voice I detest, to my name, to routinely remembering, to Castilian, over which I have no control, to feeling nostalgic for the Latin I do not know. It is trying to sink into death and being unable to sink into death. It is being and continuing to be ."