I am 13 weeks pregnant and an emergency medical technician. Rest assured that your baby is very well protected inside of that snug little environment that you have created for him/her. With that being said, falling on your hands and knees should be no cause for alarm. Your body has designed a super insulated and cushioned home to grow your bundle of joy, and that home is able to safely withstand a few bumps and nudges from time to time (just wait until you are bulging at 8 months!). Since you didn't even land on your belly, you and your baby should be fine. Pay attention to yourself, and if you start feeling any harsh and unusual cramping, spotting, or anything else that simply doesn't feel "right" to you, call your OB. Of course, if you have to ease your mind about the situation, with or without any unusual symptoms, call your OB and let him/her know what happened. As a medical specialist, he/she is better equipped than anyone to let you know if you need to be seen by a hospital.