hard to say, because both sound plausible. what makes me think it was an attack was the results after you woke, the taste and the colour of your saliva. i've been able to see shapes and spirits, never a green mist, but i've read about things like that.
the sleep paralysis is very commonly confused with haunting. you're still asleep, but you're slowly waking up, when we go into deep sleep, our body's sort of lock in place. [i guess you already know this though] for this reason, our eyes may open but our mind is still in the dream, and our body still asleep, so you may see images from your dreams in reality, making people think they're ghosts.
myself, i think it could be a bit of both, you woke up and was in sleep paralysis and a spirit was entering your room. though if this specter disappeared when you woke up i'd like to say dream. it's the taste thing. then again, you could be making it all up so who can really say.