Keep it Straight,
I'm just like your friend. If I have a gap of more than 4 weeks of flying, I still get sick. I've been flying for 6 years and am approaching 150 hours.
Some other things that I have learned over the years:
If you're heavily into your Flight Sim's (like me) this makes your brain believe that you can fly a plane without experiencing the movements associated with real flying. So when you get into a real plane you are not expecting to be thrown around - and it all comes to you as a surprise.
