Oh my goodness...my youngest does this
She's my 5th, and my sister has 4, and I had never seen anything like it the first time it happened!
She was about 8 months. I went up the stairs & shut the baby gate behind me (husband was down there with kiddos)...she crawled after me, pulled up on the gate & SCREAMED - one long, exhale & then like a silent cry of sorts...of course, we all ran to her, but she never took another breath & collasped to the floor right as we got to her...it was all so fast. I snatched her up & she came to, all limp, she was scared & whimpering & clinging to me. I took her to her doctor, because I was sure she had a seizure! She examined her, and then told me the craziest thing - "it's 100% behavioral"
Of course, I didn't believe her at all!! Not my sweet angel lol
Well, it started happening more often - especially if she was tired, feeling unwell, hungry, etc...it could be over anything but getting buckled into the car seat & not getting her way were her biggest triggers
At one of her last check ups, the doctor asked me about it & I told her, no it's been months since she's had an episode - we (literally) give her everything she wants lol...if I can't, I find something equally as desirable: candy, Popsicles, a new movie for the car, whatever...
She's almost 2 now & I can redirect her quick enough to prevent them...I can kind of tell when it's about to happen. Also, she NEVER misses a meal or a nap lol!
Oh, and one time she was at the beginning of a freak out & doing that thing where she doesn't breathe in, so I blew in her face to get her inhale...ugh, it was so terrible!! She started gasping, then choked & hiccuped for about 30 minutes, crying hysterically the whole time. I seriously found it easier to redirect, or if it was past that point, letting her "faint" in my arms...then it was over & she would usually just rest peacefully versus crying for so long.