See here: Re: Wider-ranging
Also, look at the context in which you saw this. For instance:
When being assessed for medical care, I fell through the cracks and failed to meet the required targets.
what is the meaning of (I fell right through the cracks)
In AmE, to "fall through the cracks" means that you were ignored, neglected or overlooked.
"The Child Protective Services department is so under-staffed that many documented cases of child abuse fall through the cracks and never get investigated."
To fall through the cracks often refers to someone's experience in a large bureaucracy, like a health system, a welfare system, or a justice system.
In a system meant to handle large numbers of people, a self-perpetuating network of rules, regulations, paperwork, protocol, etc. usually builds up. Personal interaction becomes subservient to the filling in of paperwork, the meeting of deadlines, etc.
To fall through the cracks, is to be unable to receive help from such a system, not because one does not need or deserve help, but because one's case is lost in the maze of the 'system' and/or because one's individual circumstance does not meet the exacting criteria of that system.
I hope this is helpful,
I've heard this idiom before and always thought it could have a more personal meaning. Is it really only applicable in the spirit of bureaucracy? The image it seems to conjur with me is a more general sense of neglect and abandonment, as in 'to disappear'.