Yep it is to do with the gforce & what your body/the object feels.
Dr. Phil has given you the explanation you need to understand..
A good test for any of you out there is, the next time you fly, put a glass of red wine on the table & when you realise you are turning (normally sun moving through windows) look at the liquid's position in relation to the rim of the glass. In the turn it should be the same as if it were on a bar top in the terminal building.
After the experiment you can have a nice drink.
Many people sitting in the middle seats of a wide body don't realise the movements of the aeroplane for a similar reason.
For the same reason, when doing instrument flying you are trained to not trust your senses & trust your instruments. The instructor can put you in positions where you think you are upright but in reality you are in a turn either climbing or descending.
When younger I used to think it was due to the sticky food from the lower tray acting as glue!
Happy Landings
