fall behind

fall apart

To be emotionally in crisis.

fall around

To fall over continually, especially through drunkenness, clumsiness, or incompetence.

fall asleep

To be affected by paresthesia; to go numb.

fall at the last hurdle

To fail near the end of an activity, a project, etc.

fall between the cracks

To wind up in an unexpected situation which is, inadvertently, invisible to or not handled by whatever process one had hoped to be subject to; to be overlooked.

fall between two stools

To fit into neither of two categories and, hence, be neglected or fail.

fall by the wayside

To fail to be completed, particularly for lack of interest; to be left out, to suffer from neglect.

fall for

To be fooled by; to walk into (a trap) or respond to (a scam or trick).