Insomnia is defined as “repeated difficulty with sleep initiation, duration, or quality, despite adequate time and opportunity for sleep, that results in some form of daytime impairment,” according to the National Classification of Sleep Disorders.

In other words, it’s a term that can refer to a wide range of sleepless situations, from those who lie awake all night to those who wake up and can’t get back to sleep. (Sleep problems that don’t fall under this umbrella include sleep apnea and restless legs syndrome.) Insomnia can last a few weeks or months, and for some it’s a lifelong challenge.

One thing is certain: “Insomnia is a symptom of an underlying problem,” says Susie Esther, a specialist in sleep-disorder medicine. So if your doctor gives you that label, she will want to look for the cause, which might be depression, anxiety, or physical issues. Treating those underlying issues can often cure the insomnia.