Medicare and Medicaid are the biggest element of our most serious national problem: crushing federal debt. Washington has evaded the debt crisis for the past two years but can’t do so any longer. The Congressional Budget Office recently projected that “spending on the major health care programs would grow from more than 5% of GDP today to almost 10% in 2037 and would continue to increase thereafter.” Without changes, health care alone will consume more of the federal budget than all discretionary spending does now — defense, law enforcement, courts, and all regulatory agencies. Every time we have to reconcile taxes and spending or approve a federal budget or raise the debt limit, we’ll face the inescapable need to cut Medicare’s and Medicaid’s growth. And every time an elected official whispers such a thing, large groups of citizens will scream.

MORE: The next entitlement crisis: Medicaid spending threatens education

They’ll yell even louder as 2013 progresses and we all come to grips with the Affordable Care Act. The employer mandate takes effect on Jan. 1, 2014, so companies are deciding what kind of health insurance, if any, to offer employees. We can be certain that some employers who currently offer insurance will find they can save money by dropping it and paying the required penalty. America’s largest private medical insurer, WellPoint (WLP), is planning on it, says executive vice president Lori Beer: “There will be a transition from employer-based [coverage] to more consumers as purchasers.”

If you think workers will be surprised when their coverage disappears, just wait until they discover they’ll be violating federal law if they don’t buy health insurance on their own. Employers who’ve raised this issue with employees report that many of them, especially lower-paid ones, are simply incredulous. No one can force them to spend their hard-earned dollars on insurance if they don’t want to, workers say — but they’re wrong. Low-paid workers might be able to get subsidies for the premiums they’ll have to pay on the state insurance exchanges, if they can figure out how. The exchanges are scheduled to open for enrollment on Oct. 1, but so far only 20 states are setting them up. Many of the other states’ exchanges will have to be run by Washington, and it still isn’t clear how they will work.

Unpleasant surprises may even await workers who do not have employer-sponsored coverage. That’s because a business that fails to offer insurance to workers can avoid paying any penalties if it has fewer than 31 full-time employees. So lots of small-business owners I’ve talked with are figuring out how to replace full-time employees with part-timers. They know it’s bad for employees but feel they have no choice.

MORE: Is Obamacare killing medical device startups?

While implementing the ACA will be a growing topic through 2013, it is only the beginning of health care taking over the economy. From 17.9% of GDP in 2011, total health care spending will grow to 19.6% in 2021, the Centers for Medicare and Medicaid Services project. Health care, already the economy’s largest sector by far and proportionally (and absolutely) much bigger than any other nation’s health care sector, will keep growing faster than GDP. It can’t do that forever, but with 10,000 baby boomers turning 65 every day, how the growth ends up becoming sustainable is not remotely clear.

Medicine will keep improving, and as the population ages, more people will want the best care available; we cannot possibly keep providing it as we plan to, yet no one will want to say no. As the costs of health care become increasingly socialized, healthy taxpayers will increasingly see obese smokers as the enemy. The conflicts will be personal, painful, and powerful — and we’ll try not to confront them.

One day we will wake up, and we’ll have become the health care nation.

This story is from the January 14, 2013 issue of Fortune.