This is something that happens to a select number of people everywhere. It's the phenomenon known as "knocking." The type of people who experience this are usually very anxious or stressed with their everyday lives.

It starts off as a light tugging in the chest. You'll feel as if there's something hammering away at your heart. This sort of feeling isn't anything that hasn't been felt before. However, one should be wary after experiencing this. It isn't too long after when the knocking is felt.

The knocking will most likely happen at night before you go to sleep. People who have experience knocking say that it happens almost as soon as their head touches the pillow. Their heart will pound so hard and fast that it almost feels as if it's being pulled out. Next comes the sound of knocking. It's said to sound like someone knocking on a door from inside your head. The worst part about it is that it plays a trick on the already anxious mind. The victim will probably be focusing too hard on their heart rate to think about where the sound could be coming from. They'll most likely think that the sound is coming from somewhere inside their place of residence, from any and all angles.

It truly is a terrifying thing. Research is still being done on it. We can only hope that it eventually leads to something conclusive.