Q: Car shuts off after loud tapping but starts back up

I just got a mustang about a month ago (may 2017). My mustang started making a tapping noise about 2days ago. Then 2days later it shut off on me when I got to a laundry mat soon as I parked but I didn't have enough time to put the the car in park before it shut off automatically. I also notice my cars oil gauge was jumping as if no oil was in the car. But when I check the dipstick it shows that it's over full by at least a inch or two. Since it couldn't start up we got it towed the next day to the house. But now it started this morning but the tapping is still there. I was told either the rod knocking. Or the head gasket is gone. I was also told my antifreeze maybe mixing with oil which is why it shows over amount of oil on dipstick. In the end it's a loud knock but the car is still starting.

My car has 185000 miles.
My car has an automatic transmission.