I paid off my mortgage last August by selling $90K worth of VTSAX when it was at 70.
All the numbers and analysis said don't pay it off and keep it invested.
Today's closing price on VTSAX was 58.
I feel calm, relaxed and I sold some bonds and made a retirement contribution of $10K to buy back VTSAX at 58 this afternoon.
I will keep buying back in whenever the market tanks again over the next few months or years.
But I won't ever do it with borrowed money.