Research suggests dogs may be able perceive changes leading up to their own deaths, based on observed physical response
Possible Awareness
Sensing impending decline seems gradual. Old/sick dogs losing function begin sleeping more
Gradual Process
Some dying dogs may dig/scratch beds, pace to find comfort spots for resting/sleeping - perhaps instinctually preparing their "nest" site.
Preparing Nest
As death nears, a few days before, some more social dogs stop eating to visit/interact with human family members, like saying goodbye.
Saying Goodbye
Dogs can keenly sense human emotions/danger etc, so they may apply that perception to bodily changes happening internally too
Sixth Sense Strength
Whether dogs know every detail or not, they settle in resting places as the weariness of age/illness fatigue them
Peace and Rest
Try not to disturb a resting terminally ill pet. Comfort them if distressed, but otherwise let them pass naturally
With Understanding