Although its name is very vivid, exploding head syndrome isn't painful.

It's where you hear a loud noise right before you fall asleep or wake up -- and other people don't hear it. It may sound like fireworks, a bomb exploding, or a loud crash. Some people have described it as a gunshot, cymbals crashing, or a lightning strike.

Even though it doesn't hurt, it can cause confusion. As it's happening, you may think you're in the midst of a heart attack or stroke.

Sometimes, you might just hear a loud sound. Other times, you may also have a flash of light or a muscle twitch at the same time.

Episodes could come every so often. You may hear several sounds in one night. You could have a lot of them in a short period, then none for a long time.