So many people, like Tim Ferriss, have experimented with their own bodies over the last two decades (and come back to share results with their audiences) that terms like serotonin and endorphins, far from being the domain of medical students or nutritionists, are now commonly understood in at least a vague way. There are chemicals and hormones that our bodies release in order to make us feel a certain way or want to do certain things. What highly productive people do is use that knowledge to their advantage, taking care to load up on certain chemicals when necessary while also avoiding the possibilities of addiction to those chemicals.
Dopamine: this neurotransmitter sends messages between brain cells. It motivates you to take action and gives you pleasure when you achieve something. Rewards for achievement are good...until their too much of a good thing. As with anything pleasurable, humans can sometimes keep reaching for more of the pleasurable thing, but if this happens too often your brain will begin to rewire to accommodate this, creating an addiction. While the most serious cases of dopamine addiction can be seen in the use of heroin or coke, in which enormous amounts of dopamine are created, the one that even children are being exposed to these days is likes on social media. Studies have shown that these offer micro "hits" of dopamine and as such can cause addictive behavior as well. While the dark side of dopamine is important to mention, we can't get away from the fact that ultimately it's a positive part of our brain chemistry. If you're lacking motivation, you're probably lacking dopamine.
Oxytocin: this hormone is sometimes called the "cuddle" or "love" hormone. It makes us feel good when we are physically close to fellow humans, even sometimes with pets. Like dopamine, it has a dark side, but that doesn't come from too much of the chemical, as with dopamine. Rather it is the environment you are in that will make you feel positive and cuddly, or suspicious of others (for example, social or ethnic groups you are not ordinarily bonded to) or dismayed over past failed intimacy or bonding with others (be it friends or family).
In women oxytocin is particularly important, as it causes contractions in the uterus during labor and helps to shrink it after delivery. It also is what stimulates the release of breast milk for feeding infants.
Serotonin: like dopamine, serotonin is a neurotransmitter. Like oxytocin, it also has a mainstream nickname: the "happy" hormone. If we feel lonely or depressed, it is likely that we have a deficit of serotonin. Serotonin also works with melatonin to regulate our internal clocks and sleep cycles. In recent years the medical community has attempted to treat depression by regulating serotonin levels using what are called SSRIs (selective serotonin reuptake inhibitors). Serotonin does seem to be a sexual inhibitor, though, so a significant percentage of those using SSRIs have experienced sexual dysfunction as a result of using these drugs.
Endorphins: anyone familiar with exercise knows about endorphins. After lengthy, vigorous physical activity, endorphins are released into our system that make us feel good and want to continue on in the activity. Since they relieve stress and pain, they function similarly to opiods, though they are much more powerful: one type of this chemical is known to have twenty-times the capability of morphine in blocking pain. As we've seen with other key chemicals, there's a downside to too many endorphins. If you have too many for too long a time you can be on edge. Your body will assume that something painful is about to happen, and a fight-or-flight reflex will be triggered for even the smallest of things.
All four of these chemicals are important parts of your productive life. As such you should ensure that you're producing them in regular amounts to help you speed and assist your day.
The most productive people use this knowledge to make sure that, on a daily basis, they are doing what they can to maintain healthy levels of these chemicals. You can't wait for it to happen to you and what matters for some may not work for others, i.e. some people don't like spicy food, or aren't as comfortable hugging others. Put together a routine that works for you and you'll find that your body will start regularly assisting your will in accomplishing and achieving what you need to do.