My pdoc has said that if the symptom lasts for 4 days it is likely a bipolar thing and not a reactive mood state. I like his perspective.

So when I have a bad day and it bleeds into another bad day and I can't trace it to a specific event I start to think that it may be related to my bipolar. I try to "sleep on it" to give me some distance from the problem. If I can't sleep for more than 1 night, I also suspect a more permanent mood state may be coming upon me. In the end, I try the 4 day rule.

I know that some people have more volatile moods than I do. I consider myself stable. So what I said above relates to me and is not a prescription for all. I try to see myself as having a normal range of emotion while knowing that the shadow of bipolar is always on my shoulder.