A childhood belief about sleeping

For several years when I was a child, I shared a bed with my sister who was 7 years older than myself. And one night I got the bright idea to try sleeping with the covers pulled over my head. Well, my sister told me not to sleep with it that high, because I might smother. So I pulled it down below my nose. I thought that was fine, but she told me that it was STILL too high! So I pulled it down to my neck. Again, still too high, so I went to mid chest, and then before it was over, I had the covers down to my waist. After she told me that was good, she turned out the lights and went to sleep, leaving me to freeze. And like an idiot I stayed that way the whole night, too scared to cover up because I thought I'd die if I did. Sadly, it never even occured to me that I'd never smothered to death before...