The colloquial phrase like death warmed up (also like death warmed over) is an extended form of like death, attested in the mid-17th century and meaning extremely ill, or exhausted.
The earliest occurrences of the phrase like death warmed up, like death warmed over, that I have found are as follows, in chronological order:
1-: From The Pharisees (Garden City (New York) and Toronto: Doubleday, Page & Company, 1922), by the British journalist, novelist, barrister and politician Muriel Morgan Gibbon (1887-1975):
For once his self-assurance seemed to have vanished and even his control deserted him. He came down to breakfast looking, as his young sister said, “like death warmed up”; half way through the meal he pushed back his chair and left the room, to return three minutes later and repeat the performance. No wonder his mother was upset!
2-: From a letter to the Editor, published in The Halifax Daily Courier & Guardian (Halifax, Yorkshire, England) of Friday 15th December 1922:
Singing a Crime.
Halifax, Dec. 14, 1922.
Sir,—Allow me to protest against making criminals of our youths for simply singing a few choruses on a Sunday night. What are our lads to do? There are no amusements. The parks or the Moor is not available for games on Sunday, yet. Neither can they all go and let steam off on a Saturday afternoon at the football match: some are working. The powers that be must be lacking in commonsense when they take notice of some cantankerous individual who has forgotten his youth and is more like death warmed up than a human being. And why do they make fish of one and flesh of another? If they want to lock somebody up there is the Salvation Amy, who sing every Sunday night, not on the Moor, but in the main street. And what a stupid excuse the magistrate said about people having a look round and see a bit of Nature—mind you at 7 p.m., when it is pitch dark. What is wrong with the man in blue that they should employ plain clothes men just as though they were after a murderer or a dealer in dope? Evidently our police service would sooner manufacture cases than prevent them. It is time they opened the cinemas and other entertainments and find interest or games, instead of leaving only one game open on a Sunday —promiscuous love-making or flirting.— Yours,
3 & 4-: From The Sick Pearl, by the Welsh novelist Berta Ruck (1878-1978), published in several U.S. newspapers in 1924—for example in the Morning World-Herald (Omaha, Nebraska):
3-: On Friday 28th March 1924 (Chapter 17):
To that touchingly hoarse appeal that languid drawl responded only. “How can any one start feeling intrigued before they have had a single cocktail and when they are only that minute over feeling like death warmed up with flu? How can I know what I really want to do?”
4-: On Wednesday 2nd April 1924 (Chapter 21):
Lying helpless in that bunk, growing more feeble with every whop and flop, feeling, as Claude might have said, like death warmed up, she could not think in terms of nights and days.
5-: From the column Gadflights, by ‘Gadfly’, published in the Daily Herald (London, England) of Monday 1st November 1926:
The doctor diagnosed a touch of ’flu. I thought he was at least half right, considering that I was rather like death warmed up.
6-: From The Harvest of Hunger, by the Yorkshire playwright James Richard Gregson (1889-1981), published in The Leeds Mercury (Leeds, Yorkshire, England) of Saturday 17th March 1928:
“It has come true, lass!” shouted Abram! “He’s clammin’ like we did! He’s stopping at t’Mitre Hotel on t’doctor’s orders! I went in an’ ordered a rump steak for my dinner, an’ then I saw him! He looked like Death warmed up! An’ does ta know what he were trying to eat? Plain boiled rice! Rice without milk or without sugar! That’s his diet! An’ he has a job to digest that! An’ theer he is, starving in t’midst o’ plenty, in spite of all his brass! If tha’d nobbut seen his face while he watched me eat t’biggest dinner I’ve had! I had it to spite him!”
“But why should he be starvin’?” asked the slow and wondering Ellen.
“Becoss he’s been so keen on makin’ brass that he’s neglected his innards until they won’t work right! He’s browt it on hissen, tha sees!”
Ellen nodded with solemn satisfaction and said, “Whatsoever a man sows——.”
7-: From Chapter 27 of Man Madness, by the British author and journalist May Christie (1890-1946), published in the Wilmington Morning News (Wilmington, Delaware, USA) of Wednesday 19th December 1928:
“Gosh! When I was jour age even, I’d have had more spirit!”
“I don’t know what you mean”, Kitty jerked her slim shoulders uneasily.
“Come off it! There’s something the matter when a young girl, who ought to have a string of beaux and the time of her life, looks like death warmed up! I’d have more pluck!”