A shock

I let Inca out this morning, it was extremely cold & frosty, she did or I thought she was about to roll which she likes to do. I heard a yelp & then she was motionless. I rushed out, she was limp & I lifted her & brought her in. A few minutes later she sat up, she didn't seem to realise anything had happened. This was taken just before we got in the car to go to the vets to be checked over, her heart & lungs seemed okay, I just have to monitor how she is & go back if I've any concerns.
She doesn't look as if anything was wrong with her, but seeing her this morning gave me an  awful shock.