I've had episodes of sleep paralysis from the time since I was about 12. Sometimes, I'd have a sense that a Terrible Man was in the room, hovering over me. I'd sometimes feel like I was choking and unable to breathe. I'd fight against it with all my might, but I couldn't move.

It's a recognized sleep disorder; however, it's not considered dangerous, just upsetting.

From WebMD: Sleep paralysis is a feeling of being conscious but unable to move. It occurs when a person passes between stages of wakefulness and sleep. During these transitions, you may be unable to move or speak for a few seconds up to a few minutes. Some people may also feel pressure or a sense of choking.

Once it was adequately explained to me, I stopped fighting it. As I lay there, unable to move, I'd focus on breathing and within a minute or so, my brain waves and my body would move back into sync and I'd be fully awake and able to move. It's not scary any more. Perhaps if it's fully explained to your mother, and if she accepts it, she can stop being afraid and you won't have to interrupt your own sleep to check on her.

First couple times it happened, it freaked me out. Thought I was dying. I was afraid to go to sleep. My mother knew a psychiatric nurse who gave a complete Freudian analysis that was all about sex. It wasn't. It's not a psychiatric disorder. It's neurological. Once that was all explained, I was okay, eventhough I continued to have episodes.

Is your mom able to have an evaluation at a sleep disorder clinic?

Here's the full WebMD article: Sleep Paralysis Symptoms, Treatment, and Causes