Yes, I believe bipolar is a spectrum mental illness in that there's a wide spectrum that people fall along yet are all bipolar.

I have bipolar 2, and my understanding and experience with it is that you have deep depressions and low highs known as hypomania. In all the years I've had bipolar [35+ now], I've never been mania, but have been hypomanic for days on end. I don't believe that mania is determined by length of time, but by severity of the high. In hypomania a person feels great, has the racing thoughts and pressured speech, but isn't so out of control that they're off mortgaging the house and booking passage on a cruise around the world for their entire family.

I also believe that bipolar can and is cyclical, and a person can be fine for a period of time, and the bumped up or down into mania/hypomania or depression. In my case, it always seems to be precipitated by something going on in my life that is stressful.

From my research on bipolar, most people who have drinking or drug problems have underlying mood disorders that they're trying to medicate.