Nobody functions well when short on shut-eye. Some tried-and-true tactics for those moments when your lack of sleep catches up with you:
Constantly oversleeping because of bad nights? Turn up the volume on your alarm clock – and set it to that annoying alarm rather than the radio. Make sure you're setting it for a reasonable hour and not an overly optimistic one. You might even place the alarm clock across the room so that you have to get out of bed to turn it off.
Groggy all day long? Perk up with a caffeinated beverage or two if need be, but then switch to decaf or no-caf after lunchtime. Too much caffeine will overstimulate your body and lead to sleeping problems at night – and if you limit the java jolts, the caffeine will be more effective when you do have a cup. Also try to do your most detail-oriented tasks early in the day, when you're sharpest.
Dragging midday? If you're at work, try sneaking a 15-minute nap in your car during break time. Taking a short stroll outside the building can also revive you. If you're in a long meeting, bring a cold drink to help you stay alert and sit near an open window, if possible. If you're at home, try to rest or nap during your child's naptime.