You'll feel much better if you stretch your back backward. Sometimes herniated discs can slip back in to place.
この場合、次のような言い方ができますよ。
ーYou'll feel much better if you stretch your back backward. Sometimes herniated discs can slip back in to place.
「背中を反らせたら楽だよ。飛び出た椎間板が元に戻ることもあるよ」
to stretch one's back backward で「背中を反らす」
herniated discs「椎間板ヘルニア」
ご参考まで!