Seeing as everyone experiences SP differently, there is a good chance that what you experience was in fact SP.

Do not worry about swallowing. The focus of trying to achieve SP is to not do anything that you wouldn't do if you were asleep. But when you sleep, you swallow anyways so that you don't drown in your own saliva. So swallow as much as you want, but keep it natural.

Many people experience the numbness of the limbs during SP, so that is also another reason you could have experienced SP. When you are in SP, (Sorry if I am incorrect) you haven't fully made a transition into the dream yet. (If that isn't true, then it is because you might not have been into SP 100%. So that could explain why you could still hear external noise.

By the way, I love Avatar too