Atonic: Without normal muscle tone or strength. An atonic seizure is one in which the person suddenly loses muscle tone and strength; the person cannot sit or stand upright and, unless supported, falls down. SLIDESHOW Brain Food Pictures: What to Eat to Boost Focus See Slideshow From Brain and Nervous System Resources Understanding Plexiform Neurofibromas Featured Centers What Are the Best PsA Treatments for You?Understanding Biologics 10 Things People With Depression Wish You Knew Health Solutions From Our Sponsors Shot-Free MS Treatment Your Child and COVID-19