Here are some examples:
* "The meeting was mind-numbingly boring, I almost fell asleep."
* "The paperwork was mind-numbingly tedious, I couldn't focus for more than five minutes at a time."
* "The traffic was mind-numbingly slow, I felt like I was stuck in a time warp."
Essentially, something that is "mind-numbingly" dull or overwhelming causes a feeling of mental fatigue or disconnect.