The British-English adjective powfagged means extremely tired.

For example, the British playwright Charlotte Keatley (born 1960) used this adjective in the following passage from Our Father (London: Bloomsbury Publishing Plc, 2012):

Priest The walls of thy cell can never be opened until thy death, Catherine…
Cath Aye. When may I be put in there?
Priest The men of the village are bringing stones from the hill, and the stonemason awaits my orders.
Cath – They’ll be right powfagged after.

The adjective powfagged originated in Lancashire, a county of north-western England, on the Irish Sea, and is from:
– the noun pow, variant of poll, denoting a person’s head;
– the adjective fagged, meaning extremely tired.

The earliest occurrences of the adjective powfagged that I have found are as follows, in chronological order:

1-: From The Bolton Chronicle (Bolton, Lancashire, England) of Saturday 28^th May 1859—the lecturer proposed a different etymology:

“WHOAMLY ¹ GOSSIP.”

On Tuesday evening, Mr. J. T. Staton ² gave his lecture entitled “Whoamly Gossip abeawt th’ Lancashire dialect,” before a tolerably large audience in the Concert Hall. […] There was a word in very common use in this neighbourhood,—the word “powfag.” It did not occur in Tim Bobbin’s works ³, nor was it used in many places in Lancashire. The origin of the word was curious. In ancient times, when a person became tired with mowing, he was said to fag at the pole—the pole of the scythe; subsequently he was said to be pole-fagged; and as in Lancashire the word pole was pronounced “pow,” it easily became corrupted into “powfag.” The word was used to imply exhaustion. Thus, if two people were wrestling, one would say to the other, “By th’ mass, aw’ll powfag thee!” that was, he would exhaust him. If a person, a woman particularly, belonging to the broad-spoken class, had gained the summit of a hill and was out of breath, she would say, coming to a stand, “Eh dear, awm gradely powfagged.”

¹ The adjective whoamly is a dialectal variant of homely.
² James Taylor Staton (1817-1875) was a Lancashire printer, newspaper publisher and editor, journalist and dialect writer.
³ Tim Bobbin was the pseudonym of the Lancashire poet and dialect writer John Collier (1708-1786).

2-: From The Blackburn Times (Blackburn, Lancashire, England) of Saturday 15^th February 1862:

THE LANCASHIRE DIALECT.
A LECTURE BY MR. JOHN SALISBURY FOR THE RELIEF FUND.

In the Blackburn Times of last week we noticed that Mr. Salisbury had delivered a lecture on the above subject, in the Rechabites’-hall, forming one of the free course now occupying the attention of a great body of the public, on Saturday evenings. The attendance on the occasion was so large—as it has been at all the lectures—that Mr. Salisbury, at the request of some friends, determined to repeat the lecture at the Theatre Royal, and to apply the proceeds to the benefit of the fund stated. […]
Mr. John Salisbury […] gave some amusing anecdotes, showing that the Lancashire dialect was imperfectly known. A great many of our Lancashire words are little understood by even Lancashire people; for instance, take the word “powfagged.” It does not appear in Tim Bobbin’s work, nor is it to be met with in many Lancashire places. It corresponds in meaning with the word exhaust. Thus, if two people are as we say “rostling,” one will say to the other, “I’ll powfag tha, owd lad;” if a person was going up a steep hill, and felt exhausted, he would say “I’m gradely powfagged;” or if a stout lady was carrying one of her pledges of love till she was tired, she would say, handing it to her lord and master, “Here, te this child, I’m gradely powfagged.”

3.1 & 3.2-: From Tales and Sketches of Lancashire Life (Manchester: John Heywood – London: Simpkin, Marshall & Co. – 1862?), by the Lancashire weaver, journalist and dialect writer Benjamin Brierley (1825-1896):

3.1-: From A “Strike” Adventure:

“Let’s turn back,” said Dick Samson, who began to be afraid lest they should be surrounded by an army of “spies” and denounced to the Ashton magistrates if they were still in power. “Ther’s no tellin what wi may leet on if wi go’n any fur. Ther’s some sort o’ rumption gooin on ’ith country, no deawt, an’ wi’st be gettin lurked, or lawmt, or powfagged some road, so let’s turn back while us booans are whul.” (Dick was a coward at the bottom, though he was noisy at meetings.)

3.2-: From Glossary of the Lancashire Dialect:

Powfagged, wearied.

4.1 & 4.2-: From Lancashire Rhymes: Or, Homely Pictures of the People (Manchester: John Heywood – London: Simpkin, Marshall & Co. – 1864?), by Samuel Laycock:

4.1-: From Aw’ve Hard Wark to Howd up mi Yed:

Th’ Muses han hard wark to live,
One’s bin hamper’d an’ powfag’d so long.

4.2-: From Glossarial Notes and Illustrations:

Powfagged. Wearied out in both body and mind. This may refer to either head or hand.