She had been driven over the edge by the separation from her husband. 丈夫离她而去，把她逼向疯狂的边缘。
A series of professional failures finally drove him over the edge.
It was the lack of sleep that drove me over the edge.
When people are under so much stress, a simple thing like their car breaking down can push them over the edge.
The infection that brings someone to A&E may be the thing that pushes them over the edge, health-wise.
See also: edge noun (ALMOST)