If you start the day feeling positive but feel yourself growing increasingly glum as it slugs along, you’re not alone. A new study using Twitter [1] to track daily, global mood swings found that people tend to have two peaks [2], happiness-wise: early in the morning and then again around midnight, reports the Huffington Post. Sociologists at Cornell University tracked more than half a billion tweets [2] from more than 2 million Twitter users across the globe over two years. Relying on language-monitoring software, they found that people tend to be happiest relatively early in the morning, but that good mood deteriorates as the day continues…