Once as a teenager - and I was convinced that there was a tiny demon pulling at the bottom of my duvet while it was happening. I could hear a little growling sound and a tugging sensation at my feet
. (edit: Yes, we had a dog. No, it wasn't the dog!)
It's not always an anxiety thing, it can be down to bad or messed up sleep patterns, it used to often be called "Night Nurse's Paralysis" because it's common in nurses who work varying shift patterns and have to regularly switch from day shifts to night shifts and back again.
I suspect it happened to me when I was a teen because my sleep pattern was ****ing stupid... I used to sleep 2am - 6am and then "nap" 4pm - 7pm. Honestly I didn't have anything resembling a normal sleep pattern until I had kids. Ironically.