We each, as spiritual beings, have the native ability to simply know things sometimes. What you know is what you know. A car owner might know, that his or her car is going to start breaking down soon, so will sell or trade it in on a newer car. We are each non-physical, immortal, spiritual beings and are not the mortal, physical, human body we operate (like a car) and view in a mirror, so can sometimes be aware of when death of this human body is near.