Thrown out of Sim whilst flying

I was having a good flight oround New Zealand then for reasons unknown I was thrown out and back to the desk top. This has happened twice, any advice would be welcome.
My Peripherals sensitivity problem was sorted out thanks to the help from you guys.

What plane? What were you doing at the time? Always at the same point?

Hi sorry for late reply. Its C150 flying straight and level well trimed on both throw outs