Upstairs, in his own room, Dorian Gray was lying on a sofa, with terror in every tingling fiber of his body. Life had suddenly become too hideous a burden for him to bear. The dreadful death of the unlucky beater, shot in the thicket like a wild animal, had seemed to him to prefigure death for himself also.

– Oscar Wilde

The Picture of Dorian Gray, Chapter 18. Dorian fears that death is coming for him. So he becomes more and more anxious and terrified over every little thing. He feels the death of the man in a shooting accident – James Vane, thought Dorian doesn’t know this yet – is foreshadowing of his own death.