If you think the eurozone debt crisis is bad, perhaps you should worry about Japan.

While European countries worry about their debt level when their debt-to-GDP ratios go beyond 100 percent, yet Japan's debt-to-GDP ratio is an astounding 230 percent.

Japanese government debt is the "mother of all bubbles," Brad McFadden, founder of the investment newsletter, Daily Trading Report, told CNBC. "The big problem for the Japanese is that they're addicted to debt and much more so than the Europeans."

Japanese domestic investors have traditionally financed that debt, but the eurozone crisis has prompted foreigners to turn to Japanese government bonds, or JGBs, as a safe haven. Foreigners owned about 8.3 percent of JGBs as of March, the most since 1979 when the central bank started keeping records.

That increase of foreign ownership may make the bonds more vulnerable to yield spikes, according to CNBC.

Half of the government's revenue goes to paying interest. It doesn't take a rocket scientist to see that rates start increasing, Japan could spend 100 percent of its revenues just on paying interest, McFadden told CNBC.

Japan's government debt is unsustainable, agrees economist Andy Xie, according to CNBC. Its interest expense is a quarter of its budget. "If the bond yield rises to 2 percent, the interest expense would surpass the total expected tax revenue (this year) of 42.3 trillion yen," Xie says.

In an attempt to control government debt, Japan's lower house of parliament voted to double the consumption tax to 10 percent.

Japan has maintained its huge debt and low interest rates by borrowing from its own people and its domestic companies, notes the Christian Science Monitor. However, its population is aging and its savings rate is falling.

Japan, the second largest foreign holder of American government debt, could be forced to sell U.S. Treasurys to meet interest payments. That, in turn, could raise rates for American bonds, causing more difficulties for U.S. finances, explains the Christian Science Monitor.