simulator sickness with aerobatic flight sim

i'm developing a flight sim game where you have to fly close to the ground (20meters AGL or so and 100mph) and get trough gates (red bull air race kind of thing). i'm getting as motion sick as if i was in the real airplane (full marks for realism but not nice as i can only fly about 1 minute before i want to throw up)

is this going to get better over time? am i doing something wrong? is a high speed, low level close to the ground flying game just a really bad idea?