If I were Cook and Flower I wouldn't be too worried yet. Any team can get into one of those 'perfect storm' moments where a particualr bowler, usually a 'mercurial' one like Johnson, just gets it right.
Think South Africa at the Oval 1994.
In fact, think South Africa at the hands of Mitchell Johnson in early 2009(?)
My precise facts may be a bit fuzzy, but I think it went something like:
Aus got 600-odd on a relatively placid pitch in Durban. Then they were 50-odd for three in no time, but effectively five down as Smith and Kallis both retired hurt, broken hand fending off a brute of a ball in Smith's case and a split chin in Kallis' case.
The worry is that Johnson has a 'wonder series' and just keeps doing this. As a dyed in the wool england fan, I still wouldn't mind watching it, though. I bowled left-arm quickish when I played cricket and I love nothing more than watching someone bowling quick and aggressively, to the point where they become unplayable.