Sleep-Less Nights

Your body is a big fan of consistency, which includes going to bed and waking up at the same times each day. Disrupting its rhythm in either direction—getting less or more sleep—can throw off your body and make you tired. On top of that, sleep cycles are typically about 90 minutes long; if you sleep in and end up awaking in the middle of one, it can leave you groggy all day.

MORE: Why Extra Sleep Makes You Sleepy