I will say that if it is on both sides, and appears symmetrical, I am going to have to say that Demodex is a lot less likely.
Some dogs get an idiopathic/unknown symmetrical seasonal alopecia (hair loss). I have treated it with melatonin for those clients that are really bugged by it, but it usually comes and goes... with no real reason and no real cure.
Sometimes intact animals (although I don't know if your is or not
) will get it with hormone changes. Like I said earlier... unfortunately, it could be anything.
And if the vomiting continues, I'd be worried about that as well. I hope it was a one time thing!