Theory:

     I watched dumbstruck as a hundred carefully sorted documents came raining down in a fluttery cascade, coins bounced to a variety of noisy oblivions and the now-lidless tin of tobacco rolled crazily across the concourse disgorging its contents as it went.
 
     “My tobacco!” I cried in horror, thinking what I would have to pay for that much tobacco in England now that another Budget had come and gone, and then changed the cry to “My finger! My finger!” as I discovered that I had gashed my finger on the zip and was shedding blood in a lavish manner. (I am not very good around flowing blood generally, but when it’s my own — well, I think hysterics are fully justified.) Confused and unable to help, my hair went into panic mode.
Explanation:
 
The narrator was shocked to see all his documents flying across the hall. To the narrator's dismay, there were about a hundred carefully arranged documents. All his coins went bouncing and rolling noisily across the floor in all directions. And to make things worse, his tobacco tin's lid got removed when it fell, and the container rolled across the lobby with the tobacco flowing out as it moved.

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Tobacco tin with a pipe
 
The narrator was disturbed, given that he would have to spend a considerable amount to get that much tobacco in England. Moreover, England had revised its budget recently and hence, getting adequate amount tobacco is going to cost him more. He pondered over all these concerns when he cried "my tobacco!" in horror and pain.

However, the cry "my tobacco!" changed very quickly into "my fingers!" when he discovered that his finger was bleeding. He had hurt his finger when the zip had come undone abruptly. Now that his finger was bleeding, he went into a panic mode. The narrator never felt good at the sight of blood in general, and given that the blood in question came out from his fingers, he becomes quite distraught and hysterical.
 
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The narrator goes into panic mode
 
Meanings of difficult words from the paragraphs:
 
S.No
Words
Meanings
1
DumbstruckSo shocked or surprised as to be unable to speak
2
SortedOrganized, arranged, or dealt with satisfactorily
3
FlutteryMove with a light irregular or trembling motion
4
Cascade
Pour downwards rapidly and in large quantities
5
OblivionsState of being unseen or unaware
6
Concourse
A large open area inside or in front of a public building
7
Disgorging
Pour something out
8
BudgetIn the UK, the official statement that the government makes about how much it will collect in taxes and spend on public services in the future
9
GashedMake a long, deep cut in
10
HystericsA wildly emotional and exaggerated reaction
Reference:
National Council of Educational Research and Training (2006). Moments. Accidental Tourist- Bill Bryson (pp. 56-59). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.