Bipolar Disorder

Bipolar I and II and Bipolar Spectrum Disorder are not differentiated by their depression though some say the depression is more severe with Bipolar Disorder.  The real difference is the mood swing and the presence of mania or hypomania.
To make a diagnosis of Bipolar I, mania is essential.  This disorder is the classic, Manic Depressive Disorder. Prior to the introduction of medications Mania could last up to 4 months and people could die from it.
Mania is essentially a week of euphoric high associated with grandiosity, dramatically increased energy, a sense of incredible well being and a bit of a used car salesman on late night tv personality change.  The woman becomes Wonder Woman and the man becomes Mr. Studsky.  Sexual promiscuity is common. One does not need sleep.  Insomnia is the norm.  High energy, high productivity and flights of fancy.  It has been called a poor man's cocaine trip.
The key feature is the person has not done cocaine or other mood altering substances and the experience of mania appears to occur de novo, like a common cold. One can't ascribe any particular trigger or event.  Things were normal and then suddenly they weren't. It's like a car that went from 60 km an hour to 260 km an hour for no apparent reason.
The flip side is depression.
My 60 year old friend who became manic went from being everyone's grandfather, quiet, somewhat depressed businessman to overnight being one of the men Elliott Ness might chase. He showed up with a red shirt and a real pearl handle six shooter stuffed in his pants and told me that he had to do a job to get some money because the women couldn't resist him and he planned to do some real partying.  He was talking a mile a minute, had never had more than a couple of beer and denied drugs but was he anything but the humble quiet man I knew.  I later learned from the police that he was suspected in an arson a few weeks later and that 20 years earlier the he'd been suspected in a string of arsons that occurred over a few week period.  A month later he was the same old guy but no longer 'high', however he did have a new set of wheels and wouldn't talk about the past or the police.  A mutual acquaintenance said he just changed like a Jekyll and Mr Hyde, one day talking about the young women after him and the next day back at the shop same old reclusive guys.
I'll never forget the Manic woman I first saw in the hospital. They're quite unforgettable and have a penchant for red. She was in a red dress and greeted me coming on the ward, this very beautiful and voluptuous woman, sayin, "you want to have sex with me. I can see you looking at my breast like a man who wants to strip me naked. The nurse is a lesbian and she wants me too but she'd never admit." She was speaking a mile and minute and literally bouncing off the walls.
I've always maintained that my grandmother could diagnose mania as well as any doctor and if a normal person couldn't see the person was really bizarre or odd then it wasn't yet full blown mania.
By contrast hypomania is attenuated. It's mostly 'irritability' rather than euphoria though I've seen some patients with Bipolar II who will described days of simple unexplained joy interrupting their otherwise unmitigated general depression.  The common variety is days of disturbed sleep usually insomnia, coupled by racing thoughts, and particularly ugly irritability.  These people are sarcastic usually and especially judgemental and easily triggered.
To make a diagnosis of Bipolar I , Manic Depression, the Mania needs to last a week.  By contrast the diagnosis of Hypomania can be made if there are mood swings and the period of irritability lasts for only days.  There's some definite wiggle room in the Bipolar II diagnosis.
Often if a person doesn't quite make it to Bipolar II diagnosis for whatever reason they get called Bipolar Spectrum Disorder and these most commonly get lumped into the diagnosis of Bipolar II rather than being called 'atypical depression."
DSM5 The Diagnositic and Statisitical Manual of the American Psychiatric Association has a list of features for each which are used to make the diagnosis but clinically this, to my mind, is what is most important to watch for.