It's also the severity of depression vs mania, even though both are present. With bipolar 1 the symptoms of mania are the most severe, and with bipolar 2 it's the depression that's most severe. Bipolar 2 can be misdiagnosed as major depressive disorder. That's how it was with me. The depression was so huge that it was hard for me to tell if the hypomania was actually mania or just not being crushingly depressed so it took a pdoc who was really paying attention to my symptoms to figure it out.