Everyone goes through periods of deep sadness and grief. These feelings usually fade away within a few days or weeks, depending on the circumstances. But profound sadness that lasts more than two weeks and affects your ability to function may be a sign of depression.

Some of the common symptoms of depression are:

  • deep feelings of sadness
  • dark moods
  • feelings of worthlessness or hopelessness
  • appetite changes
  • sleep changes
  • lack of energy
  • inability to concentrate
  • difficulty getting through your normal activities
  • lack of interest in things you used to enjoy
  • withdrawing from friends
  • preoccupation with death or thoughts of self-harm

Depression affects everyone differently, and you might only have some of these symptoms. You may also have other symptoms that aren’t listed here. Keep in mind that it’s also normal to have some of these symptoms from time to time without having depression.

But if they start to impact your day-to-day life, they may be the result of depression.

There are many types of depression. While they share some common symptoms, they also have some key differences.

Here’s a look at nine types of depression and how they affect people.

Major depression is also known as major depressive disorder, classic depression, or unipolar depression. It’s fairly common — about 16.2 million adults in the U.S. have experienced at least one major depressive episode.

People with major depression experience symptoms most of the day, every day. Like many mental health conditions, it has little to do with what’s happening around you. You can have a loving family, tons of friends, and a dream job. You can have the kind of life that others envy and still have depression.

Even if there’s no obvious reason for your depression, that doesn’t mean it’s not real or that you can simply tough it out.

It’s a severe form of depression that causes symptoms such as:

  • despondency, gloom, or grief
  • difficulty sleeping or sleeping too much
  • lack of energy and fatigue
  • loss of appetite or overeating
  • unexplained aches and pains
  • loss of interest in formerly pleasurable activities
  • lack of concentration, memory problems, and inability to make decisions
  • feelings of worthlessness or hopelessness
  • constant worry and anxiety
  • thoughts of death, self-harm, or suicide

These symptoms can last weeks or even months. Some people might have a single episode of major depression, while others experience it throughout their life. Regardless of how long its symptoms last, major depression can cause problems in your relationships and daily activities.

Persistent depressive disorder is depression that lasts for two years or more. It’s also called dysthymia or chronic depression. Persistent depression might not feel as intense as major depression, but it can still strain relationships and make daily tasks difficult.

Some symptoms of persistent depression include:

  • deep sadness or hopelessness
  • low self-esteem or feelings of inadequacy
  • lack of interest in things you once enjoyed
  • appetite changes
  • changes to sleep patterns or low energy
  • concentration and memory problems
  • difficulty functioning at school or work
  • inability to feel joy, even at happy occasions
  • social withdrawal

Though it’s a long-term type of depression, the severity of symptoms can become less intense for months at a time before worsening again. Some people also have episodes of major depression before or while they have persistent depressive disorder. This is called double depression.

Persistent depression lasts for years at a time, so people with this type of depression may start to feel like their symptoms are just part of their normal outlook on life.

Manic depression consists of periods of mania or hypomania, where you feel very happy, alternating with episodes of depression. Manic depression is an outdated name for bipolar disorder.

In order to be diagnosed with bipolar I disorder, you have to experience an episode of mania that lasts for seven days, or less if hospitalization is required. You may experience a depressive episode before or following the manic episode.

Depressive episodes have the same symptoms as major depression, including:

  • feelings of sadness or emptiness
  • lack of energy
  • fatigue
  • sleep problems
  • trouble concentrating
  • decreased activity
  • loss of interest in formerly enjoyable activities
  • suicidal thoughts

Signs of a manic phase include:

  • high energy
  • reduced sleep
  • irritability
  • racing thoughts and speech
  • grandiose thinking
  • increased self-esteem and confidence
  • unusual, risky, and self-destructive behavior
  • feeling elated, “high,” or euphoric

In severe cases, episodes can include hallucinations and delusions. Hypomania is a less severe form of mania. You can also have mixed episodes in which you have symptoms of both mania and depression.

Some people with major depression also go through periods of losing touch with reality. This is known as psychosis, which can involve hallucinations and delusions. Experiencing both of these together is known clinically as major depressive disorder with psychotic features. However, some providers still refer to this phenomenon as depressive psychosis or psychotic depression.

Hallucinations are when you see, hear, smell, taste, or feel things that aren’t really there. An example of this would be hearing voices or seeing people who aren’t present. A delusion is a closely held belief that’s clearly false or doesn’t make sense. But to someone experiencing psychosis, all of these things are very real and true.

Depression with psychosis can cause physical symptoms as well, including problems sitting still or slowed physical movements.