I have sleep apnea and used to wake up short of breath some times. Before I got a CPAP machine, there was a period when I experienced sleep paralysis episodes. In some cases I experienced the sounds of fast running steps approaching my bed sometimes that of a child, sometimes adult, which used to terrify me (of ghost presences. These episodes also coincided with my wife and kids away on vacation and I was alone at home, which added to the fear) and wake me up after breif sleep paralysis experience. After lot of post-self-analysis I figured out that my brain must have been replaying events from past to try to wake me up so I could recover from my short breath/sleep apnea situation and get more oxygen to my brain. .... my son used to run into our bedroom early in mornings after waking up from his bed (early days of his sleeping in separate bedroom), and we used to wake up to his running and jumping into our bed. Some times my wife walks up to my bed on weekends when I sleep late, to wake me up.

I believe my brain was using, what were familiar ways of me waking up to, and trying that on me to wake me up to protect me from my low oxygen situation brought upon by sleep apnea short breaths. Nevertheless, this was kind of a vicious cycle for a while even with me fairly certain of my analysis. The terror of waking up from partial sleep paralysis to such ominous 'other presence in room' irrational feeling caused a bad case of insomnia...it was not easy to fall asleep. And the insomnia in turn worsens sleep apnea and sleep paralysis episodes.

The CPAP machine helped a lot. Nevertheless is absolutely dreadful and irrationally terrifying.