The Cleveland Clinic explains sleep paralysis:

Sleep paralysis is when you can’t move any part of your body right before falling asleep or as you wake up. It happens when your body is in between stages of sleepand wakefulness. An episode is temporary and only lasts for a few seconds to a couple of minutes. It’s a type of parasomnia. You’ll likely feel scared or anxious during a sleep paralysis episode. When it ends, you may feel confused because you’ll regain movement of your body as if nothing happened.

Sleep paralysis is similar to lucid dreaming and is experienced by 7.6% of the population. Perhaps the scariest part of sleep paralysis is that sufferers often see things during episodes; often times these visions are like schizophrenic hallucinations and can be terrifying, whose than a typical nightmare because you're technically awake.

America Sanchez has gone through this personally. She describes an experience by repeating the fact that she couldn't move or talk, "as if she was paralyzed,' but her eyes were wide open during this whole experience. She remembers her eyes being open but being unable to react to what she saw. “The only thing I could see was a tall man with all black, and a mask, and he was bleeding out of his eyes.” She was scared but couldn't express it. She was basically frozen and helpless. “All I could do was stare. I was trying to get up and move, even scream and call out for my sisters but I couldn't.” 

She gets so emotional reliving this experience that I began to get emotional, I couldn't imagine how frightening this was for her, my heart would've sank. She pulls herself together and continues, “I don't know how to explain it that well, but it just felt like what people describe as lucid dream, but I wasn't in control." She compared it to being stuck in a block of ice. She just couldn't move herself no matter how hard she would try. America mentioned, “As I was struggling to move my sister noticed me and started to wake me up by shaking me. Im so glad she did. When I woke up I immediately began to cry”. 

Zoe Sanchez, America’s sister describes the experience. “When I was getting up to get water, I turned over and saw her just completely still." America began to kind of freak out herself, because it looked like America was trying to move. She said, "at first I thought she was possessed. I was low key scared. I tried waking her up." Luckily it worked. Zoe was relieved when, "she woke up." She said, "she was shaking and just started crying.”