I have always thought Fibromyalgia was just a fancy name to describe chronic pain - I was surprised to find out that it isn't just that.

It is in fact a complicated condition that presents itself in many ways, and to be honest it presents itself in symptoms that I have always been pointing towards either my Chiari or Syringomyelia.

A quote from Fibromyalgia Association UK describing Fibromyalgia.

What is Fibromyalgia?
Fibromyalgia is a chronic condition of widespread pain and profound fatigue. The pain tends to be felt as diffuse aching or burning, often described as head to toe. It may be worse at some times than at others. It may also change location, usually becoming more severe in parts of the body that are used most.

The fatigue ranges from feeling tired, to the exhaustion of a flu-like illness. It may come and go and people can suddenly feel drained of all energy – as if someone just “pulled the plug”. Fibromyalgia Syndrome (fibromyalgia for short) is a common illness. In fact, it is as common as rheumatoid arthritis and can even be more painful. People with mild to moderate cases of fibromyalgia are usually able to live a normal life, given the appropriate treatment.

If symptoms are severe, however, people may not be able to hold down a paying job or enjoy much of a social life. The name fibromyalgia is made up from “fibro” for fibrous tissues such as tendons and ligaments; “my” indicating muscles; and “algia” meaning pain.

Again, I have been surfing the net and found that the Wikipedia site provides an excellent level of information on it.

Fibromyalgia can present wide spread chronic pain and a heightened and painful response to pressure, but when Fibromyalgia is used in terms of a stand alone condition it can also present symptoms such as debilitating fatigue, sleep disturbance, joint stiffness, muscle spasms and weakness. Some patients may also report difficulty with swallowing, bowel and bladder abnormalities, numbness and tingling , and cognitive dysfunction often referred to as brain fog.

Fibromyalgia Syndrome (FMS) can also suggest conditions such as anxiety, depression and Posttraumatic Stress Disorder. Not all people with fibromyalgia experience all associated symptoms.

Fibromyalgia is estimated to affect 2-4% of the population. There is no recognized cure for fibromyalgia, but some treatments have been demonstrated by controlled clinical trials to be effective in reducing symptoms, including psychological or behavioral therapies, medications, patient education, and exercise.

It is also thought that it can be brought on by exposure to long standing stress rather than a brain dysfunction.

Brain Fog which may be characterized by impaired concentration, problems with short and long-term memory, short-term memory consolidation, impaired speed of performance, inability to multi-task, cognitive overload, diminished attention span, anxiety, and depressive symptoms.

Another suggested symptom which will relate to a lot of Chiarians is the presence of "restless leg syndrome" which I have heard mentioned so many times in discussion.

Diagnosis (From Wikipedia)

There is still debate over what should be considered essential diagnostic criteria and whether objective diagnosis is possible. The difficulty with diagnosing fibromyalgia is that, in most cases, laboratory testing appears normal and that many of the symptoms mimic those of other rheumatic conditions such as arthritis or osteoporosis. In general, most doctors diagnose patients with a process called differential diagnosis, which means that doctors consider all of the possible things that might be wrong with the patient based on the patient's symptoms, gender, age, geographic location, medical history and other factors. They then narrow down the diagnosis to the most likely one. The most widely accepted set of classification criteria for research purposes was elaborated in 1990 by the Multicenter Criteria Committee of the the American College of Rheumatology. These criteria, which are known informally as "the ACR 1990," define fibromyalgia according to the presence of the following criteria:

A history of widespread pain lasting more than three months—affecting all four quadrants of the body, i.e., both sides, and above and below the waist.
Tender points—there are 18 designated possible tender or trigger points (although a person with the disorder may feel pain in other areas as well). During diagnosis, four kilograms-force (39 newtons) of force is exerted at each of the 18 points; the patient must feel pain at 11 or more of these points for fibromyalgia to be considered.[96] Four kilograms of force is about the amount of pressure required to blanch the thumbnail when applying pressure.
The ACR criteria for classification of patients were originally established as inclusion criteria for research purposes and were not intended for clinical diagnosis, they have become the de facto diagnostic criteria in the clinical setting. It should be noted that the number of tender points that may be active at any one time may vary with time and circumstance. Since the ACR criteria were published, research with mechanical devices that exert defined pressure indicates that diagnosis of fibromyalgia cannot be done objectively by machine and requires a doctor's subjective estimate of how much pressure should be exerted. Because of these results the lead author of the ACR criteria now questions their validity and writes "The harder you press (the more you believe?), the more FM you find. Whether one believes in FM or not, tender points capture neither the distress of FM, nor the pain, nor the myriad accompanying symptoms."

Lots to think about here as I personally can see many crossovers between what I have been told are Chiari and Syringomyelia symptoms, and other symptoms that I have been experiencing for a number of years - even before I was diagnosed with Chiari et al.

Edit: I have found an explanation where the trigger points are for Fibromyalgia and have changed the picture on the post to show these.

References:
http://en.wikipedia.org/wiki/Fibromyalgia