Fall back and Fall away

Fall back verb - To move back or away (as from something difficult, dangerous, or disagreeable).

Fall away and fall back are semantically related In some cases you can use "Fall away" instead a verb "Fall back".

Fall away verb - To grow less in scope or intensity especially gradually.

Fall back and fall away are semantically related in subside topic. You can use "Fall back" instead a verb "Fall away", if it concerns topics such as return to earlier way of doing things.