[Tanya Marie Squirrel]

I believe thats very normal for the breast to "mush" out when you are on your back. I've seen some very large breasts that become soft pillows.
Your quite normal. To get them to stick up when your horizontal you need silicone. :-)

Bobbi

Correct. They mush down because natural boobs with all the connective tissue, fat, collogen etc, there is no "solid" mass. The more mass of ductile tissue, the more it may stand more upright . Gravity tends to pull them down and to the sides.

Mine, are partially upright, when on my back, the ductile tissue is fairly developed. Though they are more prominent when i am standing or sitting up.

Like bobbi said, they would have to be silicone to stay up like baloons while laying down. Even saline implants may relax a bit, i think. Though i have no implants , i cannot speak from personal experience. Though i have seen enough adult films to be a expert :p