According to theory of traditional Chinese medicine, Qi flow leads blood flow, therfore blocked Qi may cause blood stagnation. Qi and blood are from the same root that life energy is from. So sufficient Qi will cause prosperous blood, and also prosperous blood can cause sufficient Qi.
There are many kinds of bad energy within the universe and the human body; we call the bad energy Xie Qi. And any kind of disease that is caused by the stasis from qi and blood. The Xie Qi can block the circulation and cause the stasis of Zhen Qi (good energy). So therefore, we can also say that Xie Qi cause any kind of disease. Bad emotions can cause Xie Qi to gather in the human body, Xie Qi can also intrude into the human body and cause disease when a persons good energy is weak.