general problems of the 2008 BMW 550

I was driving on the freeway and the power train light came on and the car began to loose a lot of power then when I pulled to side of the road the car turned of and would not start until several attempts . I waited about 8 min then started to drive . And it does this all the time now . Then the light goes out and drives fine . But this always happens . And it's very dangerous. I've been in some tight situations.