Perhaps if the lethal blow is from the front and they are awake, you would expect defensive wounds (injuries to the hands or arms). If they are asleep, there would be no defensive wounds.
Also the angle of the blow would be different if the person is lying down than if they are standing up. If they are in bed the attacker would probably be standing to the side of the bed and striking staight down. So the blow would be perpendicular to the body. If the victim had been standing up, the attacker is likely to be standing in front or to the back and the blow is likely to be in a different place (top of the head maybe).
Not sure if that is clear or not without drawing a picture. But the main difference would be the angle of the wound, the place of the wound and the presence or absence of defensive wounds.
I am not a CSI investigator, but I am sure it is something like that....