Media Matters explains, there's simply no such figure anywhere in anything Romer has ever said -- indeed, she has said that "health care reform is an economic necessity," and that it will "allow lower unemployment".

Politifact seems to have uncovered the source of Bachmann's "5.5 million" figure, other than the nether regions of her posterior:

Obama's economic adviser -- Christina Romer, chair of the White House Council of Economic Advisers -- has never said that a tax in the health care bill would cost up to 5.5 million jobs. Republicans have used her 2007 research to develop a calculation for job losses for any type of tax increase. If you have a number for tax revenues generated, then this model will give you a number of jobs lost. But there are factors that make this type of analysis troublesome when it comes to the health care bill. Romer's 2007 research, for example, said that tax increases that fund spending for social programs tend to balance out, and economic growth stays on an even keel. Another problem is that the Republicans take tax increases that happen over 10 years and treat them as if they happen in one year, which inflates the numbers of jobs that might be lost. Finally, this particular Republican analysis includes more taxes than just the surtax of page 336; it also includes the employer mandates of page 313. We find this analysis to be problematic and contrary to how Obama's economic adviser said the model should work.

Ah, but being truthful would not be as much fun as going on national television and lying.