The real real about laying on your back

Hi ladies!

So I’ve had massive back pain, SI joint keeps slipping out, and I’ve had a rib out of place 😱 I’ve been going to the chiropractor and he’s been a god send 😁 my insurance covered some preventive stuff like this low back stretcher called the Posture Pump. It’s amazing and stretches the low lumbar BUT I have to lie on the floor on my back to use the pump. It relieves so much pain, but everyone says not to lie on your back. So what’s the real real here? I’m 23 weeks and 2 days.