The first thing you'll need to do is take the car to a very good diagnostic
shop to find out what's wrong.  It'll be nearly impossible to figure out
without a scan tool and a good technician to sort out what's happening and
why.  Once you've established what the problem is, you can determine
potential damage if not repaired and whether you'd rather repair it or not
worry about it.

It's possible you have an issue with the transmission, transmission
control module, or throtte position sensor, to name a few of the many
possibilities.