Fun fact: That "heartbeat" in your pillow is usually Pulsatile Tinnitus, a whooshing or pulsing sound in your ear in sync with your heart, caused by increased awareness of blood flow, often when lying down (especially on your side) or due to factors like high blood pressure, stress, anxiety, anemia, or ear issues like wax. While often harmless and just from being quiet and still, it can sometimes signal an underlying issue, so seeing a doctor (ENT) is best to rule out serious conditions like vessel problems or tumors.