More Americans are diagnosed with clinical depression than with any other mental health illness each year. Chances are you know someone who suffers from depression. Depression is alienating, isolating, and can be debilitating.

Recognizing the signs and symptoms of this illness can help you help someone you love. Often, those who are depressed are reluctant to seek help, or embarrassed or ashamed that they need the help at all. If you notice that something’s wrong, your willingness to talk about it may be the thing that convinces your loved one to seek treatment. Many people with depression respond very well to treatment, whether medication, therapy, or a combination of the two.

One classic sign of depression is a dramatic change in sleeping patterns. Insomnia, especially in the form of waking in the wee hours of the morning and not being able to return to sleep, is one way this can manifest. Hypersomnia–sleeping too much–can also be a sign of depression.

Another sign is a sudden change in weight–this may be gaining, or losing weight. Sudden, unusual changes in appetite are also linked to depression.

And of course, feelings of despair, hopelessness, and helplessness, especially those that seem constant or ever-worsening over time.