Dock being unresponsive along with Command/Tab

Twice so far today, my dock just died. I can't click on anything in it, Activity Monitor's CPU history dock icon doesn't animate, and command/tab doesn't work at all.

However nothing in Activity Monitor says not responding.

To fix it, I had to reboot twice, and then after that, I got a kernel panic:

Any ideas what's going on? It seems to be working fine for the moment.

Thanks.