Spit up

Ash

My 3 day old baby was put down in his bassinet for a sleep this afternoon. I slept on my bed beside him. I woke up to him coughing on his own spit. He didn’t turn his head like he does to spew. I picked him up and gave him a light tap on the back. A small amount of spit came up. I thought he was choking on it. He didn’t get upset or anybody. In fact after I changed him he fell asleep on me straight away. This gave me such a fright and now I’m too scared to lay him down. Has this happened to anyone else. Could it be reflux?