Well, I think of it as some form for lack in energy to keep the sad memories out of sight. As long as you fight to do what you have to do to manage your day, your inner keepers keep these memories in the closet. When you become tired, however, your inner keepers are too tired to hold the door to the closet for bad memories closed. The way I see this, that is why your memories comes out in the "free".

Go with these memories if you feel it is good for you. If not, you can learn to focus on something else related to relaxation exercises.

Good luck!