Fall down and Fall off

Fall down verb - Lose an upright position suddenly.

Fall off and fall down are semantically related in fall topic. In some cases you can use "Fall off" instead a verb "Fall down", when it comes to topics like fell.

Fall off verb - To turn away from a straight line or course.

Fall down and fall off are semantically related in fall topic. Sometimes you can use "Fall down" instead a verb "Fall off", if it concerns topics such as fell.