My mother never goes to the doctor for a diagnosis; she diagnoses herself, tells the doctor what’s wrong with her, and he treats her for it.
…And she’s never wrong. I mean never.
A recent study backs up my mother’s theory (and she’s not alone in that theory) that since people know their own bodies better than anyone else ever could, sometimes you have to tell the doctor he’s wrong.
Carnegie Mellon University psychologists asked 360 healthy adults age 18 to 55 to complete a basic self-assessment to determine whether how they rated their health could predict their risk of getting a cold. 
“We wanted to examine whether self-rated health predicted effective immune response in younger adults selected for their good health and whether this association was dependent on health practices and socioemotional factors,” he said in a university news release.
The results of the assessments accurately predicted participants’ susceptibility to one of the most miserable “common” ailments out there.
The psychologists concluded that doctors might benefit from asking patients to rate their own health.
“Poor self-ratings of health have been found to predict poor health trajectories in older adults, including an increased risk for mortality,” said study leader Sheldon Cohen, a professor of psychology at the university.
That link remains significant even after accounting for the effects of objective indicators of health like physical examinations, medical records, and hospitalizations.
Researchers also found the results were true even when accounting for differences across “age, sex, race, pre-challenge immunity…body mass, season, education, and income.”
The participants – clearly all good sports – were exposed to a cold virus and monitored for 5 days after filling out the survey. About one-third of them got sick. Individuals who rated their health as fair, good, or very good were more than twice as likely to develop a cold as participants who said their health was excellent. None of them rated their health as poor.
The study found no cause-and-effect link between how people rate their health and risk of a cold or any other illness, but Cohen suggested the association could be due to “subtle sensations, feelings or symptoms that signal immune system problems.”
“There are some things that we know about our bodies that aren’t easily detectable by our physicians,” he said.
An accompanying press release stated that the results hold wider implications for understanding how our perceptions of our health might impact life span, and whether self-evaluations of health might be valuable tools for predicting the likelihood of succumbing to infections. 
“UCLA School of Medicine’s Hyong Jin Cho and Michael Irwin praised the study, calling it a ‘unique contribution to the understanding of biological mechanisms of the link between self-rated health and morbidity.’ Cho and Irwin also suggested that the results raise the question of ‘whether self-rated health serves as a simple cost-effective screening tool for susceptibility to infectious or inflammatory disorders.’”
Or, maybe some people are just hypochondriacs.