Fall off and Run low

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

Run low and fall off are semantically related In some cases you can use "Run low" instead a verb "Fall off".

Run low verb - To be spent or finished.

Fall off and run low are semantically related in decrease topic. You can use "Fall off" instead a verb phrase "Run low", if it concerns topics such as grow less or make less.