Stress has aptly been called "the silent killer". It, along with other unresolved emotional issues can lead to disease as well as hinder recovery. However, I cannot accept at all the idea that most disease is emotionally rooted. I could agree that most people with chronic illness may share common traits and that stress could have contributed to their illness as well as hindered their recovery, but cannot at all agree that merely treating stress and emotional issues is the key to recovering from all diseases.
Disease is caused by a combination of toxins and insufficient nutrition at the cellular level. Once the cellular terrain has been compromised, then disease has a welcome mat for entrance. Such disease can be introduced by toxic agents such as chemical compounds and heavy metals as well as by pathogens such as bacteria and viruses. And stress and emotional issues can play a big role, but emotional issues did not in and of themselves introduce these outside disease agents. Emotional issues might prevent our body from operating optimally so that we are properly nourished and toxins are properly eliminated, but it take more than just emotional adjustments for us to nourish and cleanse ourselves at the cellular level.
A person could have the tranquility of a Buddhist Monk and would still be prone to disease - and diabetes - if they ate a crap SADS diet that included plenty of refined sugar. On the other hand, a person could otherwise eat and live pretty healthily and too much stress couold result in illness.
Thus I would say that one should by all means address stress and other emotional issues for proper healing and optimum health, but at the same time should not neglect addressing such other vital areas as natural healing (including healing herbs for specific conditions), proper diet and nutrition, cleansing and lifestyle.