1. Major depressive disorder
When you lose a loved one, or you’re facing rough circumstances, you’ll be sad for some time. Sadness, however, is generally a short-term emotion. But if you feel deep sadness for a longer duration, you could be suffering from a major depressive disorder. Feeling hollow inside is also a big red flag indicating you could be suffering from depression.

2. Bipolar I disorder
Bipolar disorder can be more intense and difficult to treat than clinical depression. If you have bipolar I, you’ll find yourself in a very excited and energetic stage. This is called a manic episode. A manic episode is so intense, you wouldn’t be able to do your normal activities.

3. Bipolar II disorder
The second type of bipolar disorder is one where you have a major depressive episode for a minimum of two weeks, accompanied by a hypomanic episode. People with Bipolar II disorders do not generally have a full-fledged manic episode and typically don’t require hospitalization.

4. Cyclothymic disorder
Cyclothymia is a mild mood disorder, in which your mood will have ups and downs. These mood swings are thankfully not as extreme as bipolar disorder. You typically go through low-level depression for a few weeks, and then a few days of hypomania. Symptoms of the cyclothymic disorder are simply depressive symptoms and manic symptoms.