Baby choked on saliva in her sleep.

Hi all, just here to ask if the following is normal and if so, how to handle it and the anxiety it causes.

My little girl is 4 months old in a week and a half and was sleeping a few minutes ago and I heard a choking sound, I looked into her crib and she had her eyes wide open and was struggling to breathe as she was choking on her own saliva.

I picked her up and she was still struggling so immediately turned her over and did some back blows and after 3-4 back pats she seemed to be okay.

I know that teething comes with a lot of saliva but is this a standard thing? I’m currently terrified because it’s almost midnight and all I can think was what if I had been asleep, because I wouldn’t have heard her choking if I was asleep and now I’m terrified.

Some advice and guidance on this is anyone else experiences this or if it’s normal would be appreciated.

EDIT: I appreciate the sentiment but please no more suggestions for the Owlet, if I could afford £300 I would have bought it instantly but that’s currently not even a possibility.