Being tired after a day of skiing is great. Being tired after a stressful job interview is normal. But feeling tired all the time is a warning sign – something is not going right in your life and in your body. Here are some of the common, but often overlooked, causes of tiredness you need to know about.

• Sleep Apnea: Everybody knows that not getting enough sleep is a sure recipe for feeling tired. Yet some people may be sleep-deprived even after spending eight hours in bed. This can happen if sleep apnea gets in the way. If you experience sleep apnea, your breathing is briefly interrupted during sleep. Sensing lack of oxygen, your brain wakes you up to begin breathing again. Each cycle lasts only a moment, and in many cases you are not even aware of these brief sleep interruptions. Yet when they repeat dozens of times every night, your brain does not have time to rest. A common telltale of sleep apnea is snoring. If your snoring is loud enough to disturb the sleep of others or yourself or if you feel shortness of breath, gasping for air or choking that awakens you from sleep, it’s time to see your doctor.

• Caffeine overload: For most of us, a cup of coffee is a part of the morning ritual. In moderate doses, caffeine can improve alertness and concentration. Yet too much caffeine can actually cause tiredness and sleepiness in some people. Keep in mind that coffee is not the only source of caffeine. Tea, chocolate, many soft drinks, and some medications are also rich in caffeine. If you suspect that excess caffeine could be a problem (particularly if you also feel jittery or restless), cut down on caffeine but do it gradually to avoid so called caffeine withdrawal syndrome.

• Dehydration: Our bodies need water to function well, be it physical or mental activity. Your fatigue can be a sign of dehydration. If you feel thirsty, you’re already dehydrated. Drink water throughout the day and more before and after physical activity.

• Unbalanced Dieting: For many of us, struggle with excess weight is a part of everyday life and dieting is a main tool we use. Yet our bodies need energy and it comes from food. Eating too little and/or eating wrong foods are common causes of fatigue. Make sure that your diet includes proteins and complex carbs and that you eat small snacks throughout a day to prevent your blood sugar from dropping too low. If you are embarking on a dieting program (generally, a good thing), make sure to discuss your plan with a doctor or a dietician – and stick to it.

• Undiagnosed Depression: Decreased energy and problems with concentration are common signs of depression. Depression is a major illness that is often brushed away as just feeling “down” or “blue”. What’s more, there is no blood test for depression, so unless you bring your concerns to your doctor’s attention, it often goes undiagnosed. Depression, however, is a serious condition. Without treatment, its symptoms may last for months and years. The good news is that the spectrum of available anti-depression medications is already quite broad and that new, hopefully even more precisely targeted, medications are in the development pipeline. Your chances of successful treatment are quite high.

• Side effect of common medications: The list of medications that are known to cause tiredness is very long. Did you recently start on a new medication? Changed the dosage? Switched from branded to generic prescription? If so, make sure to let your doctor know about your tiredness, and do it without delay. It can be a simple coincidence or an unwanted side effect. If latter, your physician may be able to recommend an alternative or change the dosage.

Keep in mind that long-lasting tiredness could also be a symptom of a serious underlying condition, such as anemia, thyroid disease, diabetes, rheumatoid arthritis, fibromyalgia, and migraine. So if you frequently or always feel tired, fatigued, exhausted, don’t brush it off – make sure to bring it up to your doctor’s attention ASAP.