I prefer to sleep on my back, and I have been sleeping on my back since high school at least. But I try not to sleep on my back anymore at all, ever.

Part of the reason is that I snore, loudly. And sleeping on your back makes you more prone to snoring. I have purchased a couple retainer like mouth devices that help. I have these plastic tubes that you insert into your nose (that don’t work at all). I try not to drink alcohol before bed, all in an effort to reduce my snoring for the sake of everyone in my household.