1
general::
Also, fall back upon. Rely on, have recourse to, as in I fall back on old friends in time of need, or When he lost his job he had to fall back upon his savings. [Mid-1800s]
American Heritage Idioms
2
general::
Phrase(s): fall back on(to) someone or something
1. Lit. to fall backwards onto someone or something. • She stumbled and fell back onto the lady behind her. • She fell back on the couch. 2. Fig. to begin to use someone or something held in reserve. • We fell back on our savings to get us through the hard times. • We had to fall back on our emergency generator.
McGrawhill's American Idioms And Phrasal Verbs