Previously, a patient had to have multiple symptoms that were medically unexplained. But the new definition does not distinguish between those that are unexplained or those associated with illness or injury. However, where there is a physical explanation for symptoms, the diagnosis requires that other criteria, such as fear and distress, are met.
The goal was to simplify the diagnosis, according to Dimsdale. One older diagnosis, somatization disorder, which is associated with sexual abuse, had a checklist of 37 symptoms and was modified three times. "Doctors throw up their hands and can't even keep the stuff straight," he said.
"To be sure, all of us get sick and die and all of us struggle with that," he said. "What we are saying is if a patient has these persistent symptoms, thoughts and behavior that takes over their life, we think it's a mental disorder and we have good treatment for that."
Today's cognitive and behavioral therapies make SSD "highly treatable," said Dimsdale.
But critics like Frances argue the new diagnosis could "mislabel" one in 6 people with cancer and heart disease; one in 4 with chronic pain and irritable bowel; and will have an astounding false positive rate of 7 percent in the general population, based on projections from the DSM-5 working groups.
"I think they have gone overboard," said Frances, who wrote an opinion piece for Psychology Today that drew 500 comments from doctors, patient advocates and those who had been dismissed for their physical complaints as hypochondriacs.
This change is important because the DSM-5, which was approved this year, will influence revisions to the World Health Organization's international classification (ICD-11), which will be finalized in 2015.
Some advocates, including Suzy Chapman, who runs a UK website monitoring the development of DSM-5 and ICD-11, are up in arms. Chapman is a caregiver for a young adult diagnosed with ME/CFS 13 years ago.
"If the clinician considers a patient is spending far too much time on the Internet researching their symptoms, or that their life has become dominated or overwhelmed by anxiety and health concerns, or that their perception of impairment exceeds what would be expected given the nature of their illness, they will now be at risk of a bolt-on mental disorder diagnosis," Chapman wrote in an email to ABCNews.com.
Those living with cancer who are diagnosed with SSD because of excessive fear of recurring disease, might delay reporting new symptoms for fear of being "perceived as "catastrophizers," said Chapman.
The DSM-5 also allows for a diagnosis of SSD when a parent is "excessively concerned" about a child's symptoms.
She also cautions that medical patients with an additional diagnosis of SSD may be disadvantaged when applying for welfare benefits, long-term disability or disability adaptations in the home or workplace.
Bridget Mildon, a 36-year-old mother of three from Salmon, Idaho, said she was misdiagnosed with "conversion disorder," an older classification of somatic disorder before doctors recently found, among other complex medical conditions, she had Sneddon syndrome, a rare neurovascular disorder that causes transient seizures or full-blown stroke.
"It took me almost five years to get a doctor to finally reevaluate and look at my symptoms from a different perspective," she said.
Mildon, who founded an advocacy organization, FND Hope, to help those with functional neurological disorders, said she does believe these anxiety illnesses exist, but some doctors misuse the labels, making patients feel "belittled and embarrassed." As a consequence, they avoid the doctor, she said.
Marianne Russo, who struggled to find a medical diagnosis for her 17-year-old with fibromyalgia, helps parents find experts and resources for their children with special needs on her Internet radio show, "The Coffee Klatch."
"When someone is not believed, it is so defeating for that person emotionally," said the Long Island, N.Y., mother. "It creates a stigma and keeps people from doing what they have to do and moving forward."
But Dimsdale defends the updated DSM, which he said is more "patient friendly" than the DSM-4, which was written 20 years ago.
"The field has moved on," he said. "People talk a lot about the DSM being the Bible of psychiatry. I see don't see it as that at all. I see it as a useful working guide to help doctors diagnose and treat patients. If it doesn't work, we'll fix it in the DSM-5.1 or DSM-6."
"Perhaps some people fear they will be labeled or mislabeled, but my perspective is that it's important to treat people who are suffering," he said. "That's what we are about."