I had once suffered from severe constipation. It took place many years ago when I was looking after wounded elder brother in hospital. I remember to this day that I was helplessly in pain at that time. Later I often had no defecation for a few days. Obviously this was very abnormal. One should defecate as regularly as one time a day. This befell on me when I commuted from my home to our county town earlier in my teaching career. I think constipation is caused either by the imbalance of yin and yang or by lack of physical exercise. I happened to have access to bananas recently, which has greatly improved my defecation.