Gear selector not working

Last night I was driving on the freeway and my gear was reading (D-drive) as it should. Well as I was driving for a period of time I do happen to look at my speed and where it shows the gear functions; it’s blank. I immediately pull over to the median and put it park, still not reading proper gear. I turn the car off for a couple of seconds and turn back on and it’s reading? That’s dangerous especially in a lot of traffic, which can cause a serious accident.