When anything turns white in an animal, its usually a sign that the heart has skipped a beat and isn't pumping properly. Happened to my dog once a couple years ago. Same thing, was running around and went limp. Was like that for 10 min. Luckily the vet is right down the street and they did an ekg and his heart was out of beat. A few minutes later it was normal and the color came back to his gums. No seizure here though. Just laid there. Scary thing. Hope all is well with your dog.
She had a seizure! Our cocker used to do it about once a year. He used to seize and sometimes throw up and then he would be fine. Its common with the breed.
My cockatiel went limp & started acting strange holding its head down. The next day he was fine.