The colloquial phrase bundle of nerves, also bag of nerves, designates someone who is extremely nervous, worried or tense.

The phrase bundle of nerves originally designated, in physiology, a set of nervous fibres bound closely together. The earliest occurrences that I have found of this physiological use are from the explanations accompanying Table XVI, published in The Appendix to Dr. Drake’s Anthropologia Nova; Or, New System of Anatomy. With Fifty-One Copper Plates (London: Printed for William and John Innys, 1728):

[page 30, column 2]: The chief bundle of Nerves tending out of the former Plexus (η) into the Spleen, which it having reach’d, reflects from thence into the bottom of the Ventricle.
[…]
[page 31, column 1]: Nerves reaching out between this Plexus and the greatest of the Mesentery. This Plexus communicates with the neighbouring Renal by (μ) and with the Stomachical by (θ). The greatest Mesenterick Plexus, out of which a great bundle of Nerves …… arising under the great Glandula of the Mesenterick, from thence is dispers’d every where [&c.].

The earliest figurative occurrence of the phrase bundle of nerves that I have found designates, with reference to this physiological sense, a hub of intense activity. It is from On the Mischiefs arising from the Use of Intensitives, by ‘Obadiah’, published in The Christian Observer (London, England) of February 1811 [Vol. 10, No. 110, page 90, column 1]—the narrator, who lived a secluded life with his uncle, a dour Quaker, has just met his natural family:

Now, Sir, you can well conceive my amazement on joining this vehement party. It seemed a new world to me. It was like the change of moving from the pole to the equator, or of quitting the Catacombs of Egypt to visit her gayest palaces. There was as much life and emotion here in a day, as in a calendar month at my uncle’s. All around me seemed to be hung upon wires, or to be a bundle of nerves.

The earliest occurrences that I have found of the phrase bundle of nerves designating someone who is extremely nervous, worried or tense are as follows, in chronological order:

1-: From Remonstrance against Lord Brougham’s Doctrine of Rebellion, by David Leahy, published in The Albion and the Star (London, England) of Thursday 11^th October 1832 [No. 598, page 2, column 1]—reprinted from the Limerick Herald:
—Notes: Lord Brougham (1778-1868) was the then Lord High Chancellor of Great Britain, and Lord Anglesey (1768-1854) was the then Lord Lieutenant of Ireland:

Are we to be told that so far as we in Ireland are concerned, the common law and Magna Charta, and the Statute of Treasons, and the Bill of Rights, are all mere moonshine; and that the only protection which we are to enjoy against a wanton suspension of the Habeas Corpus Act, is to be found in the good sense and discretion of the Marquis of Anglesey?
Concerning the manner in which his judgment will be exercised in the case, there can be no room for doubt. Equally discarding statuary enactment and judicial construction, he has reduced the matter under the jurisdiction of physical susceptibility, and proposes to determine the existence of illegal assemblies by the sensibility of a sick man’s nerves, as unerringly as an old woman foretels [sic] the approach of rain by the shooting of her corns. The following is, I presume, something like the mode in which this extraordinary test is to be applied. One twitch of the nervous system being evidence of the external existence of isolated illegality (11), it follows that the sympathy of two irritable individuals will indicate the hatching of a conspiracy, and that if three neurotic patients should happen to suffer at the same time, there must, at that instant, be a riot somewhere in the immediate neighbourhood. But if we extend the number, as we may, to a dozen or more, and suppose twelve (12) bundles of nerves to be all simultaneously agitated, no mortal can deny but that such agitation does irresistibly demonstrate the proximity of a “rebellious assembly.”
(11) It is, of course, in the recollection of the reader that Lord Anglesey, at Cork, declared that a meeting would be illegal if its proceedings disturbed the tranquillity of persons of even delicate nerves!
(12) A rebellious assembly is a meeting consisting of twelve persons or more, &c.

2-: From Passages from the History of a Wasted Life. By a Middle-Aged Man (Boston (Massachusetts): Benjamin B. Mussey and Company, 1853), by the British author John Ross Dix (b. 1811–d. in or after 1864) [page 207]:

To my dismay, on arising, I found that the use of one leg was partially gone.
Paralysis, with all its attendant horrors, stared me in the face; produced, as I well knew, by the use of tobacco. My agitation was fearful, but I did not lose my presence of mind—a rather remarkable thing, inasmuch as, bundle of nerves that I am, the most trifling fright will ordinarily bathe me in a cold sweat.

3-: From Adam Grey; Or The Blacksmith of Riverdale, by Warren T. Ashton, published in the Aurora of the Valley (Newbury, Vermont, USA) of Saturday 5^th March 1853 [Vol. 6, No. 10, page 1, column 3]—reprinted from the American Union:

Edgar was dissipated, and at the opening of our story, had completely wrecked his health and his happiness.
It was an evil day when Edgar Martin fixed an eye of love upon Minnie Grey—evil to her, doubly so to him. The youth inherited from his mother a nervous temperament and a sensitive heart, susceptible, as the flower-petal before the sharp frost of autumn, to the blight of coldness from her he loved.
He was little more than a bundle of nerves.

The earliest occurrence that I have found of the phrase bag of nerves designating someone who is extremely nervous, worried or tense is from a correspondence from Paris, France, published in The Manchester Courier, and Lancashire General Advertiser (Manchester, Lancashire, England) of Tuesday 8^th June 1880 [Vol. 56, No. 7,353, page 5, column 5]:

Rochefort is a harum scarum creature who is given to losing his temper, trembling like a man suffering from ague, and rushing into a fight as if the whole world depended upon his adversary being killed. […] It was poor Rochefort who always led the most forlorn of hopes and was nobody’s friend, not even his own. One must be intimate with this strange bag of nerves to understand his character, and those who know him as I do cannot help liking him for his very wrong-headedness, which was often base but never mercenary.