That is scary. I would be sure to make an appointment to see the dr. today.
Also, in the mean time don't be afraid to suck up some of the drool with the nasal asprirator. Just do not put it in the back of his little mouth. You may get more with a wash cloth. If he is able to be comfortable sitting/or propped up I would do that, so the drool does not pool into his mouth and back of the throat. Let us know what the dr. says too.