YOU SAID:

I sighed and fell back on the empty bed frame (my mattress had been living under the bed since that thing had looked through the windows).

INTO JAPANESE

私はため息をつき、空のベッドフレームに倒れました（私のマットレスは、窓越しに見ていたので、ベッドの下に住んでいました）。

BACK INTO ENGLISH

I sighed and fell into an empty bed frame (my mattress lived under the bed because I was looking through the window).

INTO JAPANESE

私はため息をつき、空のベッドフレームに落ちました（窓越しに見ていたので、マットレスはベッドの下に住んでいました）。

BACK INTO ENGLISH

I sighed and fell into an empty bed frame (the mattress lived under the bed because I was looking through the window).

INTO JAPANESE

私はため息をつき、空のベッドフレームに落ちました（窓越しに見ていたので、マットレスはベッドの下に住んでいました）。

BACK INTO ENGLISH

I sighed and fell into an empty bed frame (the mattress lived under the bed because I was looking through the window).