Antonym for Hypochondriac or another word completely?

For the sufferers who are afflicted with chronic pain or hidden illnesses which may or may not be diagnosed by the medical profession, there is a term for this condition:

Invisible disability

Invisible disabilities are chronic illnesses and conditions that significantly impair normal activities of daily living. In the United States, 96% of people with chronic medical conditions show no outward signs of their illness, and 10% experience symptoms that are considered disabling.

And there's an interesting article online called Chronic pain: The “invisible” disability. The author describes the frustration of managing their chronic pain, long after the illness has been diagnosed and treated

…a study by the Institute of Medicine discovered that pain can endure long after the illness or injury that caused its initial onset has been treated or healed, until it eventually evolves, or devolves, into its own disease. That is, pain is no longer indicative of another prognosis — it is the prognosis, and a disabling one at that.

However, there doesn't appear to be a single word that describes the category of silent or invisible sufferers. The only single word that comes close is stoic, which Oxford Dictionaries define as

A person who can endure pain or hardship without showing their feelings or complaining.

If the OP described this group as the antithesis of hypochondriacs the meaning would be understood. Finally, the most common phrase appears to be living with chronic pain, which is universally understood and requires no explanation.

Anosognosia. Anosognosia, also called "lack of insight," is a symptom of severe mental illness experienced by some that impairs a person's ability to understand and perceive his or her illness. It is the single largest reason why people with schizophrenia or bipolar disorder refuse medications or do not seek treatment.