Yes, I’ve noticed this too.
I have a little bubble of fluid in my spine that continually presses down on the discs, so, when one crumbles a bit as they do naturally as you get older (the process starts around age 35), if the pressure gets to a nerve, I can be immobilised by pain.
I had it all explained to me, with a walkthrough of an MRI scan, by a very informative consultant at John Radcliffe hospital in Oxford.
As I had to take some time off the first couple of times it happened, I discovered the heels effect, when I felt well enough to walk around, and CD.
The stretch on the calves and thighs, and the position my back was put into was wonderful!
As you say, you also are forced to bend differently, which also worked wonders, and I believe helps me to recover more quickly.
I’m not a doctor though, so usual disclaimers apply – you only get one back, girls – look after it!