Two weeks ago I was hit from behind as I sat at a STOP sign, foot on brake. Out of no-where car went into limp mode, check engine light on and the indicator lamp, that arrow symbol, begins to flash(fault in the automatic gearbox)? Could this be a delayed reaction from being hit?

All ideas are welcome, thanks.

 

It's something to keep in mind (the accident) but the first thing to try would be to row through the gears.
Engine running or not, move the shifter slowly through each gear from park to 1st and back again a few times. It's know to sometimes clean the PNP switch on the transmission and get rid of the dreaded flashing arrow.
It's free and easy and sometimes works. If it works you need to either enjoy your borrowed time and wait for it to happen again or disassemble, clean and lube it or replace it.