ACT and bipolar disorder

I’m looking for any materials, research and clinical considerations about usefulness of ACT with bipolar disorder. How does conceptualization of bipolar disorder actually look like in context of ACT/RFT? In my clinical practice I often encounter patients with the diagnosis of bipolar disorder type II. Their “hypomanic” episodes do not cause any difficulties in their lives. They do not engage in any activities that they regret after. I can’t see how their hypomanic episodes might impede them from reaching their ultimate goals and from living in accordance to their values. Yet, hypomanic episodes are considered in psychiatry as beeing “symptomatic” of bipolar disorder and therefore cause excessive medication. Pharmacotherapy is considered to be the primary treatment with this diagnosis.

The problem is that depressive episodes occurring in the course of bipolar disorder are considered as qualitatively different from depressive episodes that are labeled as a unipolar depression. Thus psychotherapy is in consequence considered as less effective in bipolar depression than in unipolar depression. But, are this depressions indeed qualitatively different? And does the same pathogenic mechanism that is responsible for hypomanic episodes cause depressive episodes as well? If not, are we talking about one disorder or two different disorders when we use the term “bipolar”? What kind of practical consequences (if any) would the answer to this questions have in the context of ACT/RFT?

I started to use mindfulness-based approach in the treatment of bipolar patients some time before I came across ACT. I noticed that mood changes alone are much of the problem for many of them. Many patients just compare their mood of e.g. the day before with their present mood. I’ve got the impression that much of their suffering consists of just comparing the present status with the past one or with the anticipated one.
As a therapeutic intervention in such cases I started to use my own “stairs metaphor”. I asked patients to imagine that their present mood is like a step in the flight of stairs. The stairway exists only when you look at the other steps. I asked my patients to mindfully stay where they were at the moment without looking at other steps. Then I asked them where their suffering was, what was wrong with their situation, and how they would have it improved. They discovered that their “disorder” just disappeared for the moment.
My patients often reacted in the same way no matter how they described their mental state at the beginning of the session and no matter how they scored on mood inventories. So what is exactly the essence of suffering in bipolar disorder?
That kind of intervention is of course inapplicable for highly manic patients with whom the formal and emotional contact is impossible or significantly reduced. But then, I think, we talk about psychosis, and not a mood disorder (but this is of course my personal view).