system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What exactly is happening to your legs in Restless Leg Syndrome?

That feeling you get in your legs when you're laying down and you HAVE to move them because they feel so uncomfortable, but it really never goes away. Why or how does that happen? What can you do to make it stop?

edit: just wanted to thank everybody for their comments and suggestions :) i'll be sure to try some of them out.
gpt
Okay, so everything that you do is controlled by one part of your body: your brain. Imagine that your brain is a city called Brain City. Brain City is divided into different sections based on the body activity that they control: the Cognition District, the Motor Quarter, the Reflex Precinct, etc. 

In order to execute an activity, the systems that govern each involved section of Brain City must approve and send a neurotransmitter to the action site. Think of neurotransmitters as keys that open locks that the brain must open in order to perform an activity. Different activities have different locks, which require different keys, so you end up with a variety of neurotransmitters.

For example, whenever you want to raise your right arm into the air, a very complex biological bureaucracy is doing a lot of stuff behind the scenes:

1. Certain neurons (brain cells) activate ("fire") and send a neurotransmitter called dopamine to the Motor Quarter, Office of Motor Control, Department of Arms, Right Arm Division.

2. Dopamine unlocks all of the processes involved in raising the right arm.

3. With these processes open, impulses flow into the arm muscles and cause the right arm to raise.

4. In the Cognition District, there is a little guy named Consciousness who considers himself to be the person who controls Brain City. Consciousness notices the neuron and neurotransmitter activity. 

5. Consciousness compares the pattern of firing neurons and releasing neurotransmitters to its record of past events in Brain City, and concludes that it matches the pattern that occurs whenever the brain wants to raise the right arm.

6. Consciousness makes an announcement to the rest of Brain City over a loudspeaker: "I WANT TO RAISE MY RIGHT ARM." We call these announcements "thought."

Notice anything counter-intuitive? That's right, we don't normally think of conscious thought as occurring AFTER a voluntary motion. But studies have shown that this may indeed be what happens, and that many of the things we believe to be consciously chosen actions are actually activated in the brain a fraction of a second BEFORE the section of our brain responsible for cognition.

So, with Restless Leg Syndrome, what's happening is that something is preventing the brain from using dopamine to properly unlock all the locks on the processes that control motor movement in the legs. This may be caused, for example, by an iron deficiency, as iron is involved in the creation of dopamine. And because the brain can sense that something's wrong with the legs' motor function, it triggers a stress response in the autonomic nervous system, leading to feelings of pain, discomfort, and an urge to keep moving one's legs (possibly related to the fight-or-flight response).

To make it stop, you can take a medication called a dopamine agonist (e.g. Mirapex) that will perform the function of dopamine (unlocking the locks), even if there's not enough dopamine to do so. 

EDIT: Thanks for the gold, stranger! You are fantastic!