A childhood belief about monsters

My whole childhood, all the way up until I was probably about eight or nine, every night when I would be lying in my bed trying to fall asleep, if I was laying on my side and the side of my face on my pillow, like if my ear was facedown on the pillow, and I could hear my heart beating...well, I didn't know that it was my heart beating, I thought it was the sound of this army of monsters marching to come and take me and my family away and hurt us and the only way to prevent them from coming was to not lay on my ear like that, so basically, it would be prevented if I couldn't hear them marching.