In Chapter 22 Dimmesdale seems to have recovered from his previous feebleness. He marches in the procession and is quite able to stand upright without slumping. He does not clutch his hand to his heart. In Chapter 20 he has told Chillingsworth that he no longer needs the medicine that he has been taking for years.
It was the observation of those who beheld him now, that never, since Mr. Dimmesdale first set his foot on the New England shore, had he exhibited such energy as was seen in the gait and air with which he kept his pace in the procession. There was no feebleness of step, as at other times; his frame was not bent; nor did his hand rest ominously upon his heart. Yet, if the clergyman were rightly viewed, his strength seemed not of the body. It might be spiritual, and imparted to him by angelic ministrations. It might be the exhilaration of that potent cordial, which is distilled only in the furnace-glow of earnest and long-continued thought. Or, perchance, his sensitive temperament was invigorated by the loud and piercing music, that swelled heavenward, and uplifted him on its ascending wave. Nevertheless, so abstracted was his look, it might be questioned whether Mr. Dimmesdale ever heard the music. There was his body, moving onward, and with an unaccustomed force. But where was his mind? (http://www.bartleby.com/83/22.html)
Dimmesdale had prepared a sermon for this day, but had torn it up and had rewritten it. His demeanor appears as though he is elsewhere while he is walking in the procession.
After the magistrates in their shining armor and burnished swords passed and are afforded the respect of a community and "distinguished by a ponderous sobriety," the procession of the "divine" follows.
...never since the clergyman set foot on New England shore, he exhibited such energy as was seen in the gait and air with which he kept his pace in the procession. There was no feebleness of step as at other times; his frame was not bent, nor did his hand rest omniously upon his heart. Yet, if the clergyman were rightly viewed, his strength seemed not of the body....There was his body moving onward and unaccustomed force.
Dimmesdale appears invigorated by a spiritual force or idea. When he speaks to the community, he is inspired by "a preternatural force." Thus, he sees nothing, hears nothing, but is propelled by the spiritual force of his mind and its own thoughts. Hawthorne remarks,
Men of uncommon intellect, who have grown morbid, possess this occasional power of mighty effort into which they throw the life of many days, and then are lifeless for as many more.
In this passage, Hawthorne presages the makedly moving sermon of the Reverend Dimmesdale, the spiritual realm into which the minister is elevated, a realm into which Hester and Pearl cannot enter. Hester's hopes for their escape to England are dashed when she perceives her paramour as the man "she hardly knew" now. The etheral Arthur Dimmesdale is taken to the spiritual realm which she cannot enter. Again Hester Prynne is the object of stares from the crowd; she senses the great gulf between her and Reverend Dimmesdale, and she realizes that she is further alienated as the crowd surrounds the inspired minister.
In The Scarlet Letter, Reverend Arthur Dimmesdale has felt great pangs of guilt for not confessing to being the father of Pearl, Hester Prynne's child for which she must bear the scarlet letter A. Before the procession, Dimmesdale has been in a downward trend becoming increasingly feeble and looking generally uneasy. However, when he gets up to deliver his sermon just prior to the procession, he does so with great vigor and a hot passion.
During the procession following this, his weakness which appeared gone has returned if not increased. He is so feeble that he has to be helped to the scaffold for his confession.
He is more feeble.