he is so committed to godly acts and study that he is not looking after himself as he should. In particular, their view that his frequent fastings and night time vigils are to prevent his "spiritual lamp" from being "clogged and obscured" are cited as a reason why he is becoming so emaciated and pale. Chapter 9 makes it clear that the townspeople were so concerned about Dimmesdale's health that they felt his death might be imminent, which of course lies behind the suggestion that the new doctor,Chillingworth, be placed in the same house as Dimmesdale so that he could look after him in his poor condition. 

The failing health that greatly affects Reverend Arthur Dimmesdale is described to have begun around the same time that Hester's ignonimity began. This, of course, is because the guilt and shame that ate away at his ego were causing his entire esteem to disappear. As a result, he is a weakened, almost broken man. Chillingworth is aware of this almost securely, going as far as suggesting to Dimmesdale that his illnesses are caused by otherwordly causes, mainly set in the heart. Chillingworth wants to probe Dimmesdale, and hints at sin as the potential cause of his maladies.

A bodily disease, which we look upon as whole and entire within itself, may, after all, be but a symptom of some ailment in the spiritual part. Your pardon, once again, good Sir, if my speech give the shadow of offence. You, Sir, of all men whom I have known, are he whose body is the closest conjoined, and imbued, and identified, so to speak, with the spirit whereof it is the instrument.

We know, as readers, that Dimmesdale himself is responsible for his own failing health. A man once seen by his fellow villagers as a "young divine", his Oxford education, his good looks, slovenly demeanor and soothing manners made him into a pillar of the community; a man of superstar qualities who epitomized the very essence of decency, glamour, and fascination. Dimmesdale's main flaw of character is his insistence in living up to the image that the people have made of him. He wants to be the young divine. He enjoys being looked up as an elder, even being so young. He imbibes the pleasure of feeling loved and admired; perhaps those very factors were pivotal in the development of his relationship with Hester.

Now, however, the romance is gone. Hester became pregnant, which automatically makes it obvious that he is none of the things that he has come to believe himself to be. His lack of courage to face up to what he did makes him a coward. His inability to come in Hester's defense as fiercely as he should makes him a weak man. The fact that he allows Hester to suffer the shame of his sin on her own makes him selfish. The lack of interest in being true to the promises that he makes Hester makes him pretentious. The fact that he continues to adhere to the "character" of "the young divine" of the village, makes him look even more preposterous to the witnessing eyes. All of those flaws of character are eating away his ego. It is his ego, and nothing but that, which keeps Dimmesdale ill to the point of near death. He does have problems of the heart and the soul.However, he also has the biggest of all problems which is the unwillingness to let go of the lie that he has created for Hester, for himself, and for everybody else who ever believed in him. 

Arguably, Rev. Dimmesdale's condition is psychosomatic. This means that his physical ailments stem from a very disturbed state of mind, and that the latter manifests in physical symptoms that connect to the situation that he is going through.

In his case, guilt has made him weak to the point of consistent depression. This same guilt has made him self-mutilate by carving a letter "A" on his chest. It would be benighted to ignore the collateral issues that can surface from self-mutilation, namely, infection of the wounds, bleeding out profusely, pain, discomfort, fevers associated to the wounds, and much more.

In addition to this, Dimmesdale's consistent physical and mental pain can result in an overall shutdown of the body. It is no surprise that the man could nearly point out the minute he would die. He was already dying slowly for the seven years that he kept the secret of his sins.

Chillingworth was able to tell as much. It is he who decides that Dimmesdale has somewhat of an "animal" nature, "saintly" as he may be. He also points to Dimmesdale about the sins of the soul and how they attack the body as disease.

Thus, a sickness,” continued Roger Chillingworth [..]confronting the emaciated and white-cheeked minister, with his low, dark, and misshapen figure,—“a sickness, a sore place, if we may so call it, in your spirit, hath immediately its appropriate manifestation in your bodily frame”

We know that Dimmesdale was emaciated, depressed, in pain, looking melancholy, and with every sign of illness in his body. The reason for all of this was his secret. If he did not have anything to hide, or had not been with Hester in the first place, he would have remained the "young divine" that everyone loved so much. Therefore, it is safe to argue that his illness was, indeed, psychosomatic.

In the novel, The Scarlet Letter, by Nathaniel Hawthorne, Dimmesdale feels guilty about the blame and judgement that Hester takes and suffers as a result of their indiscretions. This results in not only physical deterioration but mental anguish as well. This actually works to his advantage at first as it helps him understand the sins and sinful nature of others more clearly. However, as he preaches and confesses his weaknesses, his audience assumes he’s creating allegories for them, and they don’t believe it’s really his sin. Consequently, Dimmesdale feels even more guilty and he becomes even more ill physically, mentally, and spiritually.