Thats a really good question as that same problem is probably one of my own personal struggles. I don't claim to have it all figured out yet, but I can share with you what has helped me somewhat so far.
1. Probably the easiest helpful thing for my immediate problems are herbs, as they help you calm down enough to be able to do qigong in the first place. I have found for the Anxiety/Depression problem St. Johns Wort very useful. As for the problem of being in my head too much, I have found fish oil to be helpful, which is also recommended for the manic side of bi-polar disorder. My acupuncturist gave me some Chinese herbs for excessive heart and liver fire to help calm me down in the short term, and some herbs to build up Kidney Yin for a deeper long term calm, plus I think it helps with excessive adrenaline response. He also recommended I avoid coffee which also exacerbates adrenaline release.
2. As far as qigong goes for this problem I am currently experimenting myself and don't claim to be an expert, but can share what I have done so far. As far as still/inner qigong goes, I have found the 6 healing sounds and the Inner smile meditation which Mantak Chia teaches to be very helpful in soothing the emotions/mind, but for long term results you have to be patient and consistent. As far as moving qigong goes, I am currently doing Soft White Crane Qigong, and the 8 pieces of Brocade. These tend to be very yin forms of moving qigong, and help to relax the body and mind. The results are progressive depending on how consistent I am in my practice, baby steps, baby steps haha. Though I'm not saying that these two moving qigong techniques are the only ones that would be useful for this, as I'm sure the 5 animal sports and/or Wild Goose qigong would also be useful for this, but I'm trying to be consistent with a few rather than dabble in many.
3. As a last ditch emergency "OMG I'm loosing my mind" resort, I would recommend acupuncture. There have been a couple times that my emotions got so out of wack, and I was feeling soooo rotten, that it didn't seem to matter how much qigong or herbs I did or took, nothing seemed to help. So I went to the acupuncturist and that was a pretty good emergency fix for really acute symptoms, but let it be known that even my acupuncturist said that unless I really got a good daily schedule of qigong going, that the acupuncture would only be a temporary quick fix.
Hope this helps