It is generally recommended for pregnant women to sleep on their left side as it improves blood flow to the baby and uterus. However, if you accidentally wake up on your stomach, there is no need to panic. At 16 weeks, your baby is well-protected by the amniotic fluid and your abdominal muscles. While it's best to try and sleep on your side, occasional time spent on your stomach should not cause harm. As a larger woman, you may find it more comfortable to use additional pillows or a pregnancy pillow for support while sleeping. If you have concerns or experience any discomfort, consult with your healthcare provider for personalized advice.