How bad is it sleeping on your back?

I hear laying on left side is ideally the best. Which I try to do and of course every one rolls when sleep. But the past week I can not get comfy enough to actually sleep. I'm up alot and exhausted during the day. Past few nights I've gotten comfy on my back and sleep for hours and even past time I usually get up. (Work at a school have summers off) I know im catching up on sleep that's why sleeping in but I heard it's not good to sleep on your back. I don't want to keep doing that it was nice sleep but I've realized I sleep more when on my back.