Z Axis Went Rogue

In the middle of a carve, the router spontaneously plunged all the way through my material which made the wood break free from my clamps and the bit went across my 95% completed project. It was doing its final exterior cut and it went from about 1/8in to .88 without warning. The depth per pass was set to .04. Has anyone experienced this or know why it happened?

This happened to me when I hadn’t tightened the collet sufficiently and the bit slipped down