I have had only a few experiences with sleep paralyis. All of which were drug-induced. A couple of years ago, I began habitually using hydrocodone tablets in order to get high, or to enhance the effects of other intoxicants. (I have thankfully since stopped using recreational drugs altogether.)
Sleep paralysis experiences ususally only occured when I had taken abnormally high doses, usually when I ingested dosages of 35mg or more. After I was done enjoying the high and was ready to go to bed, I would notice "floating" sensations, often associated with Phase 1 Sleep, as well as a relaxation of the muscles. Of course, I would still remain mentally alert throughout all of this.
Soon, I would begin to notice peripheral fluttering, or tunnel vision. By the time this started, I was usually completely unable to control my muscles, and often I would start hearing my heartbeat extremely loud. It was almost like like having a bass drum in my inner ear.
In the next phase of my sleep paralysis experience, the auditory hallucinations became more vivid, more bizarre, and much more frightening.
I would hear high-frequency hums, screaming children, soft singing, and a sound which to me resembled a school bell. All of this was very vivid and very scary. I would also experience, to a limited degree, visual hallucinations, such as a red pulsing light. Eventually- usually just before I "woke up" or snapped out of it- I would hear my heartbeat, now louder than ever. It would begin to slow down, and I would notice that I was breathing less frequently. My pulse would continue to slow, with each successive beat lasting longer, until finally I awoke, gasping for air. When these things happened, I knew that I would be awake for the rest of the night.
I didn't realize how similar my experiences were to sleep paralysis until some time after I had quit using hydrocodone.