裏に何かあると思わずにはいられなかった。

bottom (or another side that is hidden from view); undersurface; opposite side; reverse side; rear; back; behind (the house); lining; inside; out of sight; behind the scenes; proof; opposite (of a prediction, common sense, etc.); inverse (of a hypothesis, etc.); bottom (of an inning); last half (of an inning)

at (place, time); in; on; during; to (direction, state); toward; into; for (purpose); because of (reason); for; with; by; from; as (i.e. in the role of); per; in; for; a (e.g. "once a month"); and; in addition to; if; although

what; how many; you-know-what; that; whatsit; what's the expression; what do you call them; what?; hey!

indicates a question (sometimes rhetorical); or; whether or not; some- (e.g. something, someone); indicates doubt, uncertainty, etc.; emphatic prefix; suffix forming adjectives or adverbs; in that way

to be (usu. of inanimate objects); to exist; to live; to have; to be located; to be equipped with; to happen; to come about

if; when; and; with; particle used for quoting (with speech, thoughts, etc.); quoting particle; promoted pawn; indicates question (sentence end)

unintentionally; reflexively; spontaneously; involuntarily; instinctively

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

to need; to want