YOU SAID:

I'm so tired. I could sleep for 12 hours.

INTO JAPANESE

疲れたわ１ ２時間も眠れなかった

BACK INTO ENGLISH

I'm tired. I haven't slept in 12 hours.

INTO JAPANESE

疲れた12時間寝てない

BACK INTO ENGLISH

I'm tired. I haven't slept in 12 hours.