Roller Coaster

What happened? asked the hospital visitor to the heavily bandaged man sitting up in bed.
Well, I went to the Amusement Park at the weekend and decided to take a ride on the roller coaster. As we came up to the top of the highest loop, I noticed a little sign by the side of the track. I tried to read it but it was very small and I couldnt make it out. I was so curious that I decided to go round again, but we went by so quickly that I couldnt see what the sign said. By now, I was determined to read that sign so I went round a third time. As we reached the top, I stood up in the car to get a better view.
And did you manage to see what the sign said this time? asked the visitor.
Yes.
What did it say?
Dont stand up in the car!