What does 不得了 (bù dé liǎo) mean in English?

Card 59HSK 2010 Level 559/1311
CARD59
PROGRESS5%
不得了
bù dé liǎo
desperately serious; disastrous; extremely; exceedingly

Reveal: Click/Space/Enter/↑↓/w/s/j/kNavigate: ←→/h/l/a/d