Anxiety, Depression & Tai Chi Therapy 
JOURNAL OF PSYCHOSOMATIC RESEARCH, 1989, VOL ID 23, ISSUE ID 2, PAGES 197-206
Relative to measurement beforehand, practice of T'ai Chi raised heart rate, increased nonadrenaline excretion in urine, and decreased salivary cortisol concentration. Relative to baseline levels, [Test Subjects] reported less tension, depression, anger, fatigue, confusion and state-anxiety; they felt more vigorous, and in general they had less total mood disturbance.  
Nursing Journal, 2002, Vol. 32, Issue 12, page 86
The physical and psychological benefits of tai chi chuan are discussed. Tai chi can be used as a therapeutic tool for improving coordination, posture and flexibility and it also can be used to reduce anxiety, depression. It is also an excellent way to handle stress.  
The Brown University Digest of Addiction Theory and Application, 2002, Vol 21, Issue 3, Page S1 [producers note: given Tai Chi is a form of Qigong, and they share common benefits, this qigong study with heroin addicts and anxiety, seems relevant to this discussion on anxiety.] 
The researchers determined that reduction of withdrawal symptoms occurred more
rapidly in the qigong group compared with the patients in the lofexidine-treated group and the nontreatment control group. From day one of the intervention, patients in the qigong group had significantly lower mean symptom scores that the other two groups (p<0.01). The qigong and medication groups had lower anxiety scores than the nontreatment group (p<0.01); the qigong group had significantly lower anxiety scores than the lofexidine-treated group (p<0.01).  
American Journal of Chinese Medicine, 1981, Vol 9, Issue 1, Pages 1-14
Psychological homeostasis refers to emotional control or tranquility. It has been stated that the biological function of human emotion and repression is primarily homeostatic. Evidence suggests that a feedback relationship exists between forms of homeostasis, and the body-mind type of therapies (including acupuncture and T'ai Chi) thus have a combined physiological, physical, and psychological effect.