The last three molecules in that chain are the main trouble-makers in classic meltdowns. When your brain loses its ability to control the movement of these chemicals and their release from nerve cells, then you are at risk of a meltdown. All three of these chemicals, which are known as "neurotransmitters," either induce the release of sugar or inhibit insulin, among several other important tasks. If you are releasing too much of these neurotransmitters in a certain organ of your brain, however (called the amygdala), then your system overloads.
In the case of dopamine, your reaction to this overload may be similar to feelings of paranoia, and you may feel that those around you are trying to hurt you in some way. In the case of norepinephrine, you may have uncontrollable feelings of anger toward them, and you may shout at them and puff yourself up in spite of knowing that these people are your friends and have not harmed you or given you any cause for anger. In the case of epinephrine, which is also known as adrenaline, you will experience feelings panic, even terror, toward anything that comes close to you, friend or foe.
This is a rough explanation based upon limited knowledge on my part, but I hope that I am close to the truth and explaining myself clearly. There are probably other factors in these meltdowns that I have not taken into account. From here, hopefully, you can take a guess as to what our situation is like during a meltdown. Because different people have different hormonal balances, different people will be affected in different ways, and people will exhibit varying degrees of control. Some people will cry, and other will not. Some people will scream, and others will not. Most, God-willing, will not attempt to attack you.
The aftermath of our meltdowns is even worse than the meltdowns themselves, at least from our perspective. A sense of humiliation or self-loathing is common. Meltdowns are not very fun at all, but, unfortunately, some immature people think that they are funny. Do not be surprised if many Aspies are strongly in favor of eugenics because of this fact.