NEW YORK (CBS 2) — If your head is throbbing, your muscles ache and your stomach is in knots. Those symptoms may not be caused by what you think. They are actually signs of depression and recognizing them early could ease the pain.

Susan Fenton said she wasn’t sure what was causing her to feel ill, until she was diagnosed and treated for depression.

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“I had a headache all the time,” Fenton told CBS 2’s Dr. Holly Phillips. “It was varying degrees of a headache, but I had it all the time. I also had diarrhea for about 10 months.”

Fenton now knows depression was causing her physical symptoms – and her cause is not unusual.

“It became very clear to me what was the illness and what was the depression after the antidepressant kicked in because all of the headache and the tummy ache and all of those symptoms went away,” Fenton said.

Of the more than 19 millions Americans estimated to suffer from depression, 80 percent also experience physical symptoms. Many people go through countless unnecessary treatments that just don’t work because they’re unaware depression is the cause.

“You can’t cut off your head and say ‘well these things are in my head,’” Fenton said. “The body acts as one.”

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“How we understand depression and really all mental illnesses is that they are illnesses of the mind which is sitting in the brain and the brain is part of your body. So all of these disorders are really physical,” Dr. Richard N. Rosenthal of St. Luke’s Roosevelt Hospital told Phillips.

In fact for some people, physical ailments are their main symptoms of depression. Some of the most common include: headaches, back pain, muscle aches, chest pain, digestive problems, fatigue, sleeping problems, change in appetite and dizziness.

Rosenthal says since depression is related to chemical changes in your brain, it may also change the way we feel pain.

“Studies have shown that depressed people have a lower pain threshold. They are more sensitive to pain,” Rosenthal said.

In many cases, treating your depression — with therapy or medicine or both — will resolve your physical symptoms, Phillips reports.

“Depression is a highly treatable illness,” Rosenthal said. “So you know it is no shame…its like any other disorder…get to your doctor, get good treatment and you will feel better.”

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