If you wake up at different times each morning, you're throwing off your internal alarm, making it harder for your body to know when to start getting sleepy. You're also giving yourself "sleep inertia," the feeling of grogginess immediately following an abrupt awakening. That feeling happens when you wake up in a particularly deep sleep cycle. The problem is that when you drift back off after hitting snooze, your body may enter a deeper sleep stage than it was in before, making the groggy feeling even worse. So even if it might feel like you're getting more rest when you lay around for that extra half hour, you're actually making yourself more tired (and probably late for work).
So what should you do instead? You may not want to hear this, but research shows that you should set your alarm for the actual time you'd like to wake up. Then get up. Every day. At the same time. Eventually, you'll retrain your body clock to get sleepy at the right time and feel awake when it's time to start your morning. Don't worry, coffee is always an option. Learn more about sleep inertia and and common sleep habits in the videos below.