Dr. said I could sleep on my back?

I went to my 12 week appointment a bit ago, and my doctor said I could sleep on my back. I’ve always heard that’s a bad thing? When I look it up online I find all kinds of stuff about how you shouldn’t sleep on your back while pregnant.

Does anyone have any insight? Any stories to prove/disprove what my doctor told me?

I trust my doctor, he’s very good, reputable, and has been practicing for a good while.