Bipolar Disorder Forum - Mixed Episodes - hypomania 1st? seasonal affective disorder

Hello,
I am the wife of a possible bipolar husband, who, so far, is only diagnosed with seasonal affective disorder. I believe very strongly that my husband is misdiagnosed.
Can you please give me some insight on mixed episodes? How long do they typically last? Does hypomania often precede a mixed episode? When the episode is over, does the person usually regret actions he did during the episode or do they continue to view their actions as rational? I see a lot of things about manic episodes and depressive episodes, but very little about mixed episodes.

For those who care to read about my husband's situation:
Six weeks ago, I came home from a weekend trip and he was gone. Every morsel of him was gone. He left nothing but his wedding band and a long robotic letter. (I have posted about this before.) In the letter, he admitted that he never took the BAR exams (lawyer exams) that he was supposed to have take the week before he left. He had me under the impression that he was taking them that week!! He said that he didnt' want to live in our state anymore, that he didnt' want to be married anymore, that he didn't want children and that he doesn't want to be a lawyer now (after having just graduated from law school.) He admits to lying about several things throughout the summer. He has enrolled back in graduate school to become a therapist, now! This all came as a total shock to me!! We had a wonderful marriage! We had just celebrated our two-year anniversary and have been together for 3 1/2 wonderful years. He was just gone, just like that. In the six-weeks that he has been gone, we have only spoken via phone once - for about five minutes. He sounded very monotone, like a robot. This is also how his letter was written - no emotion whatsoever. It's like he doesn't even care or have any remorse whatsoever! This is not my huisband!!
(I should also add that about two months before our wedding, after we had been engaged nearly a year, he did something very, very similar. He had sent me a long, robotic email, saying he was moving back to his home state - 10 hours away, dropping out of law school, joining alchoholics anonymous, getting a mediocre job and not getting married. At that time, his doctor had just changed his antidepressant, so when he stablilized three weeks later and moved back down, I chalked it up to that.) Things have been wonderful ever since, although now that I look back, I see bipolar signs all over his everyday life - though none were alarming enough to raise any eyebrows. He has written a lot of dark blogs, poems on our computer, which seem to focus on death and very, deep self-analysises and introspective topics, which are very, very deep. They don't seem like things the average person would be thinking about. He loses/gains weight often. When he gets into something, he takes it to extremes. Last year, he became obsessed with exercise and lost 90 pounds in five months! He goes through stages where he becomes very irresponsible about bills/finances/other obligations (such as tags for his car, taxes, etc.) But he isn't always like this - in fact, most of the time he is not like this.
He doesn't display much euphoria - although on occasion, out of nowhere, he does - usually only lasting for a day or a few days. I can pinpoint that he was overly euphoric earlier this summer - about 6 weeks before he left. After that, his personality changed - he was irritable, blew off job interviews (and didn't bother calling to say he wasn't coming), didn't pay several household bills, including our mortgage, withdrew socially (slightly) and stopped doing all the things that interest him - like gardening, reading, watching movies, etc. He also seemed to become forgetful, arrogant at times, down at times, etc. He wasn't his usual sweet, affectionate self, any longer. Is this a mixed episode? (He made strange comments about death verbally and seemed to have some delusional thinking. He also said in his goodbye letter that his leaving had nothing to do with me - that he was irresponsible and undependable and he needed to live alone. He said that I have been a wonderful wife and companion, but that he is ready to "move on." I am absolutely devastated. The husband I know loves me, loves our home, loves his garden, loves our friends/family and this husband has just walked out on all of this - just like that. And has moved into the same apartment complex he lived in while we dated and is back in school to become a therapist.

When we spoke via email, which we have done several times to discuss bill transfers, I tried to talk to him about his mental health. And he told me his mental health was fine and my concern was not warranted.
Please help give me some insight on mixed episodes or whether or not you think this might be one! Does it seem to fit more of a manic episode, a depressive episode or no episode at all? Thanks for any help you can give!