These kind of exercise is not as common as Yoga, but the effect to relief the body and mind from anxiety are equally encouraging, but you need to do it consistently for at least 3 months to see greater results.

Taiji is a martial art developed around 200 years ago, the original form evolve from the Chen style Taiji and evolved into the modern Yang Style Taiji. The Chen style is martial art oriented, some of the move might not be suitable for treatment purpose. While Yang style is the modern popular Taiji that remove most fast and more extreme and high difficulty movement to suite the general public.

Both Taiji and Qigong are extremely emphasize on deep breathing exercise to develop inner strength of the body - Qi. Qi is the inner power that flows around your body, accelerating your body to recover from any kind of chemical imbalance or health problems.

The theory of Qi is not recognize by most medical panel, but the Chinese has their own scientific data to prove otherwise. Traditional Chinese Medicine (TCM) and acupuncture are based on the theory of Qi and how to use it for the treatment purpose. If you want to learn martial art for self-defense and treatment for anxiety at the same time, I would highly recommend you find a good reputation master to guide you; Improper practice may lead to some annoying side effect, such as delusion.

QiGong is the stripped version of Taiji, it focused on deep breathing exercise to develop Qi, and accumulate the Qi to achieve a healthy body and mind. Most of the training method has many form of meditation - sitting, slow moving and certain standing position.

You should find the proper master to guide you through learning both Taiji or QiGong; self learning courses are not recommended before you at least have a year of guidance from the proper trainer.