So Scary!

My newborn has been gagging/ burping at random times when he is laying down (diaper change, middle of the night, etc) like he is choking on his spit up. The noises that accompany it scare the crap out of me especially in the middle of the night when he is on is back. I have to hurry and flip him over and burp him. I'm terrified he is going to choke on the spit up, if I'm going to be able to wake when i hear him do that, why it's so frequent, and if it is going to slow down or stop soon. I thought babies only spit up a few times after they eat or something?  Can anyone relate or have any advice?