Because you haven’t ever really lived without them. It’s a shock to the brain and body that they are gone and you can’t necessarily believe that you won’t ever get to see them again.
Your brain has a hard time getting used to not seeing them anymore and tries to make it sound like they are there. Your brain is in a short state of depression that is easily passable. Your heart does nothing with love, they pump blood. When your brain is in shock, you heart would skip or freeze, making it hurt. Every so often it would do this when the feeling goes through your head.
