I have experienced that feeling when I was with my father when he died, with my mother when she died, and when a beloved dog died unexpectedly. It does feel like a hole, a void. The same feeling can occur to a lesser extent when we reach the end of a very enjoyable book or movie, or even when we have to take a car that will no longer run to the junk yard, or when we have to demolish a dangerously decrepit house. I think the hole is ultimately in our brain/mind, when a favorite part of our long-term memory ceases to grow from familiar experiences, and we know that it will inevitable decline and deteriorate.