YOU SAID:

i went to school and slept

INTO JAPANESE

私は学校に行って、眠っていた

BACK INTO ENGLISH

I went to school, was sleeping

INTO JAPANESE

学校に行った私は眠っていた

BACK INTO ENGLISH

I went to school I was sleeping

INTO JAPANESE

寝て学校へ行きました

BACK INTO ENGLISH

I slept and went to school.

INTO JAPANESE

私は寝て学校に行きました。

BACK INTO ENGLISH

I slept and went to school.