Ah our 3yo did that for a while a year ago, it’s very upsetting. At least yours snaps out of it quickly, ours would go for a half hour but I managed to calm her with numbers. We would count upwards as high as we could switching places and she’d calm down. Side effect, she can count past 100 now.

Oh, also it’s apparently similar to sleep walking. Apparently they’ll do that eventually.