I can verify that one should strap in in a sim. Sitting in a jumpseat/observer position the driver was demonstrating recovery from an uncommanded roll, not long after the loss of a 737. Anyway I'd got the lap belt on but not the shoulder harness. The sim 'dived' to the left as I was looking over the co-pilots right shoulder. One instinctively rapidly leans further right as the sim 'flipped' to the left, the only trouble was the sidewall/bulkhead of the sim was still travelling towards me, with the inevitable dull thud as my head and the side wall made contact
. To say it hurt was an understatement, I genuinely saw stars, little specs of white light, and the headache afterwards!
