If I click the home button, my z axis lowers very slowly (it should be going up!!). This is all that happens. Any idea what’s going on?
Even if I hit the limit switch by hand nothing happens, just continues to lower the Z.
Did you do the machine setup in Easel?
It’s nothing software related 
Machine setup establishes the correct firmware settings in Grbl to make your machine behave.
I understand The firmware hasn’t been touched since my last calibration. I literally turned the machine back on and this problem happened. and unless the arduino re-flashed its firmware without the machine or pc even running, its settings are fine.
Ok, sorry. You didn’t make it clear that you had the machine working and this was a new problem.
Since your Z homing switch didn’t affect the homing operation you could try this:
interesting stuff thanks! I didn’t know that was possible