I'm pretty sure my boss is about to put me on a PIp in this meeting, how do you prepare?

I've been struggling with some personal things in my life my mom has cancer (only child) and he's been in and out of the hospital. So things have been a little rocky. What should I be prepared to say?

Edit: I have been documenting incidents for the past 2 months, is it too late for me to go to HR with this?