Baby went under water

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So in the bath my babe was sitting in water and I was laying next to her playing with toys on my side and my arm was behind her back, for some unknown reason she thrashed backwards, she sits up nice and sturdy so it wasn't because she isn't strong enough yet, she did it just to do it. God knows why. Anyway she went under water and she couldn't breathe and water cane shooting out of her nose and she was shaving trouble catching her breath for a minute and I nursed her and she seems fine but has anyone else's baby done this? She has done something similar before, what she did was leaned into the water and I thought she was taking a sip but she inhaled through her mouth and couldn't breathe then water came shooting out of her nose. I called the on call doctor and she was fine. But this time she went completely under. I'm not as scared as I was the first time but she didn't go under like she did this time eithet. She is being normal right now. I just wasn't sure if anyone else's baby has gone completely under and inhaled water and what they did to help