Need some help... What is it? Am I ok to drive the car tomorrow? Thanks!!!!

 

Looks to me like the cross plate at the rear of the frame rails... just a guard in case the driveshaft breaks, so it doesn't drop and hit the ground. You can drive without it. Just get your underside inspected soon... seems like you may have hit a piece of carpet on the freeway or something.

 

Thanks! Drove through a water puddle that was deeper than expected... that was maybe 3 minutes before the part went sideways and fell off in the driveway. Very much appreciate your input!