神不知鬼不觉

top secret / hush-hush

God / abbr. for 神舟[Shen2 zhou1]

deity / soul / spirit / unusual / mysterious / lively / expressive / expression / look / CL:個|个[ge4] / (slang) awesome / amazing

no; not so / (bound form) not; un-

not to know / unaware / unknowingly / fig. not to admit (defeat, hardships, tiredness etc)

to know / to be aware

ghost / demon / terrible / damnable / clever / sly / crafty / (suffix for sb with a certain vice or addiction etc) / one of the 28 constellations

unconsciously

a nap / a sleep / CL:場|场[chang2]

to feel / to find that / thinking / awake / aware