choking baby

FTM- My baby is 3 weeks old. I bottle fed him and almost an hour later he had formula coming out of his nose and bubbly spit coming out of his mouth. It sounded like he  was choking/filling his lungs with fluid. He also would stop breathing and go silent and then would caugh and then scream some more. Scariest 30 minutes of my life. I don't know if I'll be able to sleep after this. We called my sister-in-law who happens to he a NICU nurse and she said it was normal and could be reflux. My fear is that he was drowning inside or something like that. Any mammas that have gone through the same thing? My husband and I felt totally helpless. It was the worst. Now baby is sleeping as I'm holding him waking him up every two minutes to make sure he's breathing. Thanks!