From Longman Dictionary of Contemporary Englishbe on the edgebe on the edgeinformalCRAZY to be behaving in a way that makes it seem as if you are going crazy → edge
Examples from the Corpus
be on the edge• Everything blended with everything else, trees and brush and sky, and already he was on the edge of lost.• He was on the edge of the crowd, and not hiding his amusement.• Apparently I was on the edge of the crater and the main blast had gone over me.• He sped to the line for the try after the ball evaded Packman and Northampton were on the edge of defeat.• He liked the feeling they were on the edge.• They went so fast sometimes he thought they were on the edge of no-control.• They were on the edge of the mountain.• Yet people ignore the plight of, say, the several species of bat which are on the edge of extinction. 