According to WebMD, the difference between bipolar I disorder and bipolar II disorder is whether or not the patient experiences mania. Patients who suffer from bipolar I disorder experience every type of pathological emotional state associated with bipolar disorder, including mania, depression, hypomania and mixed episodes. Bipolar II disorder patients, on the other hand, do not experience mania.
WebMD states that bipolar II patients experience all of the emotional states characteristic of bipolar disorder other than mania. These mood episodes include hypomania, depression and mixed states. Hypomania is a condition similar to but less severe than mania. The symptoms of hypomania don't have as much of an impact on the patient's life as mania and can actually be beneficial, causing an increase in productivity and functioning.
Psych Central explains that during a hypomanic episode patients aren't severely impaired. They are still able to go to work, don't require hospitalization and don't experience psychotic symptoms. Bipolar II disorder patients experience severe depression before, after or even during a hypomanic episode. Depressive states and mixed episodes can be severe enough to require a bipolar II patient to be hospitalized. Between mood episodes, patients suffering from either type of bipolar disorder are often able to live normal lives.