slump

[1]	decline , slip , recede , fall (off) , drop , plunge , descend , sink , crash , collapse , dive , plummet , take/go into a nosedive/tailspin
[2]	slouch
[3]	slide down , sink
[4]	fall off , sink
[5]	decline , correct

[1]	dip , slack , drop-off , trough , depreciation , falloff , falling off , decline , downturn , downslide , recession , depression , falling-off , fall-off , fall , drop , plunge , descent , crash , collapse , failure , nosedive , tailspin
[2]	depression , economic crisis