Take A Power Nap 

You need to be alert, energized, and well-rested when exercising. If you want to complete your routine workout but lack the energy to do it, you may need to rest for a bit. For a quick energy boost and increased mental alertness, take a brief 15- to 20-minute power nap. For optimal results, power naps should be no longer than 20 minutes; otherwise, you will fall into a deep state of sleep and wake up feeling groggy rather than refreshed. Many people take a shot of espresso before their power nap. Since the effects of caffeine take 20-30 minutes to kick in, the espresso helps them feel more alert upon waking up. Power naps are a quick and effective way to increase your energy before a workout, but make sure your naps do not interfere with your regular sleep schedule.