Sometimes a strange tingling sensation is just a momentary neurological misfire. But, then again, your symptoms could foretell something more serious. That's where WebMD — a popular online medical encyclopedia — comes in. Use the app's symptom checker to, well, let's face it: probably scare yourself. But as Dr. Zachary Meisel wrote recently for TIME, an informed patient is often a better patient. So bone up on your way to the doctor's office.