2006 5.9 manual tranny

I think I screwed it up. The other day I wasn't paying attention when the wind was howling in my open window, didn't hear the engine wrapping up over 3.5, way over redline.
Right when I got off the throttle it dropped to zero, then after a few seconds it sort of started working again. But now it is acting strange. Nothing when started then sort of works, then works fine, then nothing.

What did I do? How is the signal generated and how is that converted to what you see on the gauge?