Amy Rangel, 54, has long lived with postural orthostatic tachycardia syndrome, a condition marked by a racing heartbeat, fatigue and dizzy spells. Last year, Rangel, then a math lecturer at Northern Arizona University, was suffering so much that her doctors advised her to leave her job. But her short-term disability insurer denied her claim, saying she’d failed to show she couldn’t work. As Rangel’s appeal dragged on, she was quickly approved for long-term disability. But Rangel needed the $15,000 in short-term benefits to cover her bills. “We have been living on my husband’s Social Security and our retirement savings,” she wrote me.

The public relations department at MetLife, Rangel’s group short-term disability carrier, said the company doesn’t comment on specific claims. Instead, MetLife provided me with information about common filing mistakes and the appeals process. I also spoke with Emily Brown of the nonprofit Patient Advocate Foundation and Ellen Bresnahan, president of Insurance Appeal Consultants in Burke, Virginia, which handles disability cases. Here’s what you need to know about filing a claim or appeal.

▶︎ Learn the rules. Ask your human resources department for a copy of your plan. Deadlines, says Brown, are the “low-hanging fruit when it comes to denials.” And every policy is different. Although most give you 30 days to file a claim, some give you just five business days from the first day you can’t work.

▶︎ See an M.D. ASAP. Go to your doctor, an ER or urgent care to document why you can’t work. Some possible reasons for Rangel’s denial: Her disability had no clear start; her first visit after claiming was to a physical therapist, not a cardiologist; her next was to a naturopath. “Any nontraditional treatment seems to be dismissed by insurance company doctors,” Bresnahan says.

▶︎ Keep a symptom journal. A record of your condition, if shared with your doctor, can help with a claim or appeal. Focus on the intensity, frequency, duration and functional impact of your symptoms to show they interfere with a 40-hour workweek. If you have migraines, for example, you might note that a headache prevented you from sitting at your desk or using your computer for a certain number of hours.

▶︎ Work with your doctor. “The number one mistake people make is trying to explain to the insurer in their own words why it’s wrong to deny their claim,” Bresnahan says. “The doctor needs to explain it.” Make sure your physician connects your symptoms to specific reasons you cannot work. Ask to see the statement before it’s filed.

▶︎ Don’t relax after approval. Especially in long-term disability cases, expect your insurer to regularly review your status. See your doctors as often as your insurer recommends and make sure they record your diagnoses, treatment plan and prognosis for returning to work, says Bresnahan.

▶︎ Consider extra help. You might hire a lawyer to appeal a claim denial (though many won’t handle short-term cases on a contingency basis). One other option is the Patient Advocate Foundation (patientadvocate.org), which offers free assistance.

Soon after I reached out to MetLife, the company apparently revisited Rangel’s case. In December, she got her money. Coincidence? She didn’t think so, given all the letters she said she received stating there was nothing more for her to do. Bresnahan’s advice for when a long-term claim is approved but a short-term one isn’t: “Send the long-term approval letter to the short-term people and threaten to sue for the benefits.”