Depression is the common cold of mental disorders — most people will be affected by depression in their lives either directly or indirectly, through a friend or family member. Confusion about depression is commonplace, e.g., with regard to what depression exactly is and what makes it different from just feeling down.

There is also confusion surrounding the many types of depression that people experience — unipolar depression, biological depression, manic depression, seasonal affective disorder, dysthymia, etc. There have been so many terms used to describe this set of feelings we’ve all felt at one time or another in our lives, it may be difficult to understand the difference between just being blue and having clinical depression.

Depression is characterized by a number of common symptoms. These include a persistent sad, anxious, or “empty” mood, and feelings of hopelessness or pessimism that lasts nearly every day, for weeks on end. A person who is depressed also often has feelings of guilt, worthlessness, and helplessness. They no longer take interest or pleasure in hobbies and activities that were once enjoyed; this may include things like going out with friends or even sex. Insomnia, early-morning awakening, and oversleeping are all common.

These feelings aren’t just a passing mood that goes away in a few days on its own. Instead, they stay with a person for weeks on end (at least two weeks, in order it to be diagnosed). The symptoms of depression don’t just develop out of the blue, either. They usually come on a person over the course of several weeks, a little bit at a time. It can be insidious in the subtle way that depression starts to overtake a person’s life. Some people even suffer for months from mild symptoms before it becomes full-blown depression.

Appetite and/or weight loss or overeating and weight gain may be symptoms of depression in some people. Many others experience decreased energy, fatigue, and a constant feeling of being “slowed down.” Thoughts of death or suicide are not uncommon in those suffering from severe depression. Restlessness and irritability among those who have depression is common. A person who is depressed also has difficulty concentrating, remembering, and trouble making decisions. And sometimes, persistent physical symptoms that do not respond to traditional treatments — such as headaches, digestive disorders, and chronic pain — may be signs of a depressive illness.

Feeling down or feeling like you’ve got the blues is pretty common in today’s fast-paced society. People are more stressed than ever, working longer hours than ever, for less pay than ever. It is therefore natural to not feel 100% some days. That’s completely normal.

Depression can be a gradual withdrawal from your active life.

What differentiates occasionally feeling down for a few days from depression is the severity of the symptoms listed above, and how long you’ve had the symptoms. Typically, for most depressive disorders, you need to have felt some of those symptoms for longer than two weeks. They also need to cause you a fair amount of distress in your life, and interfere with your ability to carry on your normal daily routine.

Depression is a severe disorder, and one that can often go undetected in some people’s lives because it can creep up on you. Depression doesn’t need to strike all at once; it can be a gradual and nearly unnoticeable withdrawal from your active life and enjoyment of living. Or it can be caused by a clear event, such as the breakup of a long-term relationship, a divorce, family problems, etc. Finding and understanding the causes of depression isn’t nearly as important as getting appropriate and effective treatment for it.

Grief after the death or loss of a loved one is common and not considered depression in the usual sense. Teenagers going through the usual mood swings common to that age usually don’t experience clinical depression either. Depression usually strikes adults, and twice as many women as men. It is theorized that men express their depressive feelings in more external ways that often don’t get diagnosed as depression. For example, men may spend more time or energy focused on an activity to the exclusion of all other activities, or may have difficulty controlling outbursts of rage or anger. These types of reactions can be symptoms of depression.

Learn more: Symptoms of Depression

When left untreated, clinical depression can last for over a year, with 40 to 50 percent of individuals still having symptoms sufficient to meet the diagnosis after one year.

More than 85 to 90 percent of people with depression can be treated effectively. In most cases, an individual eventually will experience a complete remission of symptoms. However, approximately 25 percent to 33 percent of those untreated will continue to have some symptoms and associated difficulty with daily life that can linger for months or years.

Even though most people can be helped by depression treatment, effective depression treatment can take months to get right. Different antidepressant medications may need to be tried and discarded until the one that works for a person is discovered. The dose may also need to be adjusted until just the right dose is found that alleviates depressive symptoms while not increasing unwanted side effects.

Some people may have only a single episode of depression. However, more than 50 percent of those affected will experience another episode. This is called recurrent depression. Left untreated, this represents a chronic disease, with each episode increasing the risk for another bout of the disease. More than 70 percent of those who have two episodes can expect to have a third, while 90 percent of individuals experiencing three episodes will have a fourth episode.

The most effective type of treatment for almost all types of depression typically consists of a combination of medication and psychotherapy. Either treatment on its own is about as half as effective than when the two treatments are combined. That means that if you’re only taking antidepressants, or are only in psychotherapy, it will generally take you twice as long to feel relief from your depressive symptoms.

In the most severe and chronic cases of depression, treatment may also include electroconvulsive therapy or hospitalization. You should talk to your mental health professional about the pros and cons of these kinds of treatments, as they may carry longer-term side effects.

Learn more: Depression Treatment