We all go through periods of low energy. Even a week of feeling more tired than usual is not uncommon.

Yet most people can tell when their fatigue feels like something more serious. If that's the case, or your fatigue gets worse or lasts longer than a week or two, it's time to see your doctor. Your fatigue might be related to an underlying illness or infection, especially if it's accompanied by symptoms, such as a low-grade fever, shortness of breath, or loss of appetite.

Other reasons to see your doctor about fatigue are if you often wake up exhausted despite sleeping well, do not feel motivated to begin the day, or struggle to do activities that are ordinarily easy. These could be symptoms of a sleep disorder or depression.

During your exam, your doctor will try to rule out issues like medication side effects. He or she also may order blood tests to determine if the fatigue is related to a specific problem, such as anemia, an underactive thyroid (hypothyroidism), or liver inflammation (hepatitis). However, don't be surprised if your doctor does not find a cause. I have found that in most cases people bounce back from fatigue after some rest and a good night's sleep.