Not sure if this is yoga related, but I suspect it to be.
Last night I slept on my back for the first time in my recollected life. It happened after doing my practice routine, and then resting in savasana. It would be a pretty big coincidence for it not to be related to the practices.
This is much healthier spinal posture than sleeping on the front or side, and I'm really glad for it to happen.
I've always been under the impression that sleeping on the left side, fetal position is the best way to sleep since it helps the digestion. The right side is better for cooling down the body and in case of insomnia. I love sleeping on the back too with svasana before turning to the left, but the front is the worst since you compress internal organs!