It's not just your imagination -- you're more irritable when you're low on zzzzs. Sleep scientist Matt Walker explains how our nightly slumber affects the emotional centers in our brains, and why we can think of sleep as first aid for our feelings. Sleeping with Science, a TED series, uncovers the facts and secrets behind our nightly slumber. Check out more episodes on TED.com: https://go.ted.com/sleepingwithscience