I recently gave a training on how negative emotions can affect the physical body.
There are examples of this in the Book of Mormon.
One is Lehi and Sariah, who were so upset when their wicked sons tied Nephi to the ship that "having suffered much grief because of their children, they were brought down, yea, even upon their sick-beds. ... even they were near to be cast with sorrow into a watery grave." (1 Nephi 18:17-18)
Another example is Zeezrom, who "lay sick...with a burning fever, which was caused by the great tribulations of his mind on account of his wickedness, for he supposed that Alma and Amulek were no more; and he supposed that they had been slain because of his iniquity. And this great sin, and his many other sins, did harrow up his mind until it did become exceedingly sore, having no deliverance; therefore he began to be scorched with a burning heat." (Alma 15:3)
Here is what Boyd K. Packer said about the connection between physical health issues and maladies of the spirit, emotions, or mindset. There is a connection. It's real.
"I recently asked a doctor of family medicine how much of his time was devoted purely to correcting physical disorders. He has a large practice, and after thoughtfully considering, he answered, 'Not more than 20 percent. The rest of the time I seem to be working on problems that very much affect the physical well-being of my patients but do not originate in the body.
'These physical disorders,' the doctor concluded, 'are merely symptoms of some other kind of trouble.'
In recent generations one after another of the major diseases has yielded to control or cure. Some very major ones still remain, but we now seem able to do something about most of them.
There is another part of us, not so tangible, but quite as real as our physical body. This intangible part of us is described as mind, emotion, intellect, temperament, and many other things. Very seldom is it described as spiritual.
But there is a spirit in man; to ignore it is to ignore reality. There are spiritual disorders, too, and spiritual diseases that can cause intense suffering.
The body and the spirit of man are bound together. Often, very often, when there are disorders, it is very difficult to tell which is which."
(Boyd K. Packer, "Balm of Gilead," Ensign, November 1977)