Soul-trouble is attended usually with great pain of body too, and so a man is wounded and distressed in every part. There is no soundness in my flesh, because of thine anger, says David. “The arrows of the Almighty are within me, the poison whereof drinketh up my spirit.” Job 6:4. Sorrow of heart contracts the natural spirits, making all their motions slow and feeble; and the poor afflicted body does usually decline and waste away; and, therefore, saith Heman, “My soul is full of troubles, and my life draweth nigh unto the grave.” In this inward distress we find our strength decay and melt, even as wax before the fire; for sorrow darkeneth the spirits, obscures the judgment, blinds the memory, as to all pleasant things, and beclouds the lucid part of the mind, causing the lamp of life to burn weakly. In this troubled condition the person cannot be without a countenance that is pale, and wan, and dejected, like one that is seized with strong fear and consternation; all his motions are sluggish, and no sprightliness nor activity remains. A merry heart doth good, like a medicine; but a broken spirit drieth the bones. Hence come those frequent complaints in Scripture: My moisture is turned into the drought of the summer: I am like a bottle in the smoke; my soul cleaveth unto the dust: my face is foul with weeping, and on my eyelid is the shadow of death. Job 16:16, 30:17, 18-19. “My bones are pierced in me, in the night seasons, and my sinews take no rest; by the great force of my disease is my garment changed. He hath cast me into the mire, and I am become like dust and ashes. Many times indeed the trouble of the soul does begin from the weakness and indisposition of the body. Long affliction, without any prospect of remedy, does, in process of time, begin to distress the soul itself. David was a man often exercised with sickness and the rage of enemies; and in all the instances almost that we meet with him in the Psalms, we may observe that the outward occasions of trouble brought him under an apprehension of the wrath of God for his sin. (Psalm 6:1, 2; and the reasons given, verses 5 and 6.) All his griefs running into this most terrible thought, that God was his enemy. As little brooks lose themselves in a great river, and change their name and nature, it most frequently happens that when our pain is long and sharp, and helpless and unavoidable, we begin to question the sincerity of our estate toward God, though at its first assault we had few doubts or fears about it. Long weakness of body makes the soul more susceptible of trouble, and uneasy thoughts.
—Timothy Rogers on Trouble of Mind. The above based on the text of Psalm 6:6-7