fall asleep

asleep at the switch

Neglectful of an important task, responsibility, or opportunity.

dead asleep

Sleeping in a deep sleep

fall apart

To be emotionally in crisis.

fall around

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

fall at the last hurdle

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

fall behind

To be late (for a regular event)

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.