Modern humans often find themselves desynchronized from their internal circadian clock, due to the requirements of work (especially night shifts ), long-distance travel, and the influence of universal indoor lighting.  Even if they have sleep debt, or feel sleepy, people can have difficulty staying asleep at the peak of their circadian cycle. Conversely they can have difficulty waking up in the trough of the cycle.  A healthy young adult entrained to the sun will (during most of the year) fall asleep a few hours after sunset, experience body temperature minimum at 6AM, and wake up a few hours after sunrise. 
On average, dogs spend about 12-to-14 hours of the 24-hour cycle sleeping. Older dogs need significant amounts of sleep simply because, as they age, living becomes more difficult. They tire out more easily and need rest in order to function properly. Puppies , like babies, spend a lot of time exhausting energy while playing and exploring their new surroundings. Because of this, they might need as much as 18-to-20 hours of sleep to recoup! And of course, all dogs need sleep, but it tends to be the bigger breeds that are known for constant dozing.
You need immediate alertness. Try a “ caffeine nap. ” Researchers at Loughborough University tested several ways to improve the alertness of drivers and found the “caffeine nap” to be the most effective method. You down a cup of coffee or other caffeinated beverage and then immediately hunker down for a 15-20 minute nap. Again, don’t go any longer than that or you’ll awaken with sleep inertia. The caffeine clears your body of adenosine, a chemical which makes you sleepy. It takes awhile for the caffeine to circulate through your system, so it doesn’t effect the quality of the nap. Instead, it kicks in in tandem with the refreshment you would feel upon awakening from a normal power nap. I’ve personally found the caffeine nap to be effective, especially when you’re crunched for time; it’s easier to get up and keeps you from the temptation of turning a 20 minute nap into an hour and a half session.