Google "borderline personality disorder" (BPD) - there are some similarities to bipolar - in that people seem to be either wildly happy or horribly sad. But that's where the similarity ends. BPD realy should be called emotional dysregulation - as people with BPD are overly senstive to everything - when people make faces at them, the way a person chews (if it's too loud), something someone said, etc. They feel emotions very, very intensely. so if someone says something to you that's not nice - you'd get over it pretty quickly. A person with BPD might completely flip out because they take it as a personal attack.
Psychiatric researchers know that people with BPD have a an enlarged part of the brain that controls emotions - but many people with BPD sufferd some kind of trauma as a child. My teenaged daughter has been diagnosed with it and I can assure you that she did not have a traumatic event as a child (she was never out of my sight, she never slept over anyone's house, the doors were never closed when older cousins were around, etc.). She has had this since she came out of the womb. She's an overly sensitve kid. She'll get furious with my husband if he brings home something for my son becuase she thinks he loves him more than her. She is learning to stop and evaluate her emotional response and consider whether her perception of an event is accurate or not.
We have some really difficult days - and then we have a lot of good days. We've also been told this is something that she will always deal with (it's worse of couse in adolescence, isn't everything?) and people with BPD can have a severe or a slight case and that it generally gets better as they get older. We've also been told that people with BPD often times have excellent careers and do well in their field but have tumultuous relationships becuase they're always making small things into giant things.
Once you get a chance to do some online research on BPD you'l find there are some questions to ask that will give you an idea if this is the disorder your husband (and now you) struggle with. There is a family tendency - and I see some of the qualities in my SIL and MIL (and to a less extent my husband). If you think this describes your husband try to get him and yourself into some counseling - and at the very least do some reading on your own so you can figure out how to work around this and deal with your own emotions. It can be overwhelming some days - and as I said there are other perfectly wonderful days!
Good luck mama - I hope this is a little bit helpful.