My baby choked last night- bad! Thank god for CPR choking classes

Meleah
My 4 week old Tatum, choked bad and I couldn't get him to breathe - turned purple was foaming out nose and mouth - thank god for our CPR choking class I fixed him but it was horrifying 
I have been crying off and on since and can't sleep 
Not sure what caused it, he had taken some gas drops medicine like 10 min prior so maybe it didn't go down all the way like normal or something - I walked away like 4 feet to grab a paper towel and I saw his legs and arms in air and thought he just woke back up so didn't even grab him at first until I realized he was thrashing cuz he couldn't breathe - he made no noise or anything 
I grabbed nose sucker and sucked out his throat and nose while I was hitting his back while he was flipped over - it felt like forever until he could breathe but shortly after he seemed normal again - I am literally traumatized - scared to set him down or look away for even a minute - I'm petrified - anyone else experienced a choking incident with your lo yet?