This has nothing to do with someone's grandmother being psychic
It's basically just relaxation. A feeling, like you can't really feel anything. I used to do it in school when I was younger, when there wasn't anything going on in class. I'd sit at my desk, and I'd basically get to a point where I couldn't feel my own body, I was perfectly still. No movement, no thoughts, nothing really audible to distract me.
It's easy enough to do. There's no special abilities involved in this. You don't have to be special or psychic to do it, and it doesn't take years to achieve unless you have the shakes. You just relax. Meditation can help as well. The BEST time for meditation as I found for myself, was always after a rigorous martial arts session. We'd all sit down at the end, and my instructor would walk around, talking to us as we sat indian-style, wrists on our knees, hands hanging loose over our knees. We'd close our eyes, and it was perfect relaxation. No thoughts, nothing. You almost feel like you're floating.
It helps me get to sleep sooner if I focus on remaining still and getting to that point where I almost feel weightless. Usually, my leg (or both) are shaking or moving around and I can't sleep. So it's just something I'll do if I remember to think about it.