Vomiting an entire feeding?

Audrey • 💙💗
Last night, my 8 day old vomitted I'm guessing 4oz at least. My milk supply has seemed to skyrocket lately as he's been eating for shorter amounts of time because I don't think he has to work as hard for it. I just don't know how much he's eating. 
Is this from over feeding? I'm a FTM and it really freaked me out. 
It all came out of him exorcist style in probably 1 second. Not a slow stream of throw up. Don't know if that makes a difference.