We usually mistake the feeling of our body temperature dropping after long hours of work as a need for sleep. In reality, we don't need to sleep - we just need a break to invigorate ourselves and get more energy. Allow me to give you a personal example:
When I was in college I used to attend class or study for 8-9 hours in a row. Naturally, this involved a lot of sitting. As the day wore on I would feel increasingly sleepy. I usually laid down on my bed upon getting home and either napped, read, or watched TV. However, as I began learning the inner science of our sleep system and the inner sleep clock, I tried a little experiment one day. Instead of going to sleep when I came home, I worked out for at least a half an hour instead. To my surprise, after just a few minutes of some light exercise, the feeling of tiredness faded away and I was able to stay awake and alert way until close to midnight. Since I found a safe and healthy way to get more energy, I was able to fit in exercise, a part-time job, a social life, and homework while earning my degree.
The moving technique worked simply by allowing my body temperature some time to return back to the normal pattern. Once it returned to normal, I no longer felt tired and the intense pressure to rest faded. This same body temperature drop when you've been exercising or pushing yourself physically for a long time. It doesn't matter WHO you are: you could take a person who is robust, athletic, and naturally energetic and put them in front of a TV for 3 hours - and THEY WILL GET TIRED! This is simply because our body temperature drops when we're NOT MOVING.
That's why the biggest antidote to feeling tired is exercise and movement, NOT SLEEP. Our body temperature is also low during the morning, which creates feelings of drowsiness and tiredness - however, most of us chose to mask this feeling by consuming large amounts of caffeine (remember what I said about the line at Dunkin Donuts?). The other main temperature drops happen in the afternoon, and in the mid-evening. Getting up and moving about, even for just 5 minutes, can boost your body temperature and re-energize you without the coffee or soda!
This material is paraphrased from Kacper Postawski, who has developed a number of techniques to "create energy from nothing." (I'm not getting paid a cent to recommend him, I just think his information is useful!)