24 weeks pregnant. i use a wedge and rolled up blanket behind me but sometimes wake up on my back. did i harm my baby? should i be worried?

Vena cava syndrome: When lying on the back in advanced pregnancy, the weight of the baby can squeeze the vena cava which transports blood back from the lower part of the body to mom's heart. That in turn leads to less blood flow to the baby and a potential concern of lack of oxygen. However, when this happens, moms start feeling sick and will turn on their left side (the v.c. runs to the right of the aorta).