Hey need not be worried. It ok , but you can avoid doing so. Sleeping on back When sleeping/lying on your back the baby and womb put pressure on the main blood vessels that supply the uterus and this can restrict blood flow/oxygen to the baby. while sleeping on side had many benefits .Experts recommend lying on your left side. It improves circulation, giving nutrient-packed blood an easier route from your heart to the placenta to nourish your baby. Lying on the left side also keeps your expanding body weight from pushing down too hard on your liver. While either side is okay, left is best. Choose wisely