Falling on your back can be very dangerous. It’s important that after you’ve fallen on your back you take the proper steps to not injure yourself further:

• Assess your body: Evaluate your condition and determine if you can move. Seek medical attention if you cannot move. 
• Apply ice: If you notice any swelling or feel pain on the area you fell on, you should put some ice on it. Apply ice for 15-20 minutes with breaks in between. 
• Take it easy: Give your body some time to rest and recover. Try to avoid activities that could strain your back further.