If you're lucky, during sleep paralysis you'd just remain
paralyzed, with no hallucinations or anything else accompanying it.
But if you arn't so lucky, well, sleep paralysis would probably be
alot more terrifiying for you then, sad to say.
That's what my first experience was like, but after that things
started to get worst. Whenever I fall into sleep paralysis, my
entire body seems to be shaked very vigorously, and whatever sounds
I hear get distorted. Eg; the engine of the SBS bus below my block
sounds like a monster roaring.
Hallucinations are less common, but still happen once in awhile.
There was once I stayed up to 4am, and while walking to my bed I
just knew I was going to get sleep paralysis after I fell asleep.
Sure enough, it happened, and was my most terrifying experience up
to date. I woke up, paralyzed, and saw a ghost coming up the stairs
towards me. After getting out of it, I grabbed my blanket and ran
to my parent's room. 
False awakenings do happen too, where you dream that you wake up,
but in fact you're still asleep and paralyzed. However the thing I
like about this is that you don't actually realize you're
paralyzed.
Unable to breathe...yea, I get that too and it seriously sucks. No
idea how this comes about, but everytime I get this I often think
that I'm going to die before I wake up.
Here's a tip to getting out of sleep paralysis mode though. Just
muster all your strength together and try to move you hand, arm,
finger (depending which you have control of) by a considerable
distance of about 5 - 10cm and you'll snap out of it.