The term "functional somatic syndromes" has been in use as an umbrella term for a collection of conditions and illnesses since before 1999, in the US, UK and in other countries.
Two of the early users, here:
A US paper:
https://www.ncbi.nlm.nih.gov/pubmed/10375340
Ann Intern Med. 1999 Jun 1;130(11):910-21.
Functional somatic syndromes.
Barsky AJ1, Borus JF.
A UK paper:
https://www.ncbi.nlm.nih.gov/pubmed/10489969
Lancet. 1999 Sep 11;354(9182):936-9.
Functional somatic syndromes: one or many?
Wessely S, Nimnuan C, Sharpe M
A search for the term on PubMed will bring up over 180 papers:
https://www.ncbi.nlm.nih.gov/pubmed/?term="functional+somatic+syndromes"
going back to 1999.
See also
August 2008
Special Report co-authored by Javier Escobar, MD, and Humberto Marin, MD, for
Psychiatric Times:
Unexplained Physical Symptoms What’s a Psychiatrist to Do?
Dr Escobar was a member of the DSM-5 Task Force and served as Task Force liaison to the Somatic Symptom Disorders Work Group:
.”
In Table 1, under the heading “Functional Somatic Syndromes (FSS)” Escobar and Marin list:
Irritable bowel syndrome, Chronic fatigue syndrome, Fibromyalgia, Multiple chemical sensitivity, Nonspecific chest pain, Premenstrual disorder, Non-ulcer dyspepsia, Repetitive strain injury, Tension headache, Temporomandibular joint disorder, Atypical facial pain, Hyperventilation syndrome, Globus syndrome, Sick building syndrome, Chronic pelvic pain, Chronic whiplash syndrome, Chronic Lyme disease, Silicone breast implant effects, Candidiasis hypersensivity, Food allergy, Gulf War syndrome, Mitral valve prolapse, Hypoglycemia, Chronic low back pain, Dizziness, Interstitial cystitis, Tinnitus, Pseudoseizures, Insomnia, Systemic yeast infection, Total allergy syndrome.