"And the first went, and poured out his vial upon the earth; and there fell a noisome and grievous sore upon the men which had the mark of the beast, and upon them which worshipped his image."The Pre-Wrath view is that the 70th Week is already over when this happens, we're already in the mysterious extra month of Daniel 12.
I feel the link the first Bowl has to the Mark supports my view that the Seven Bowls span the second half of the 70th week. I believe this happens only a matter of months at the very most after the Mark is instituted.
I think it's some sort of physical side effect of taking The Mark itself.