This is very common when travelling by
train. If another train next to yours starts moving, your brain might decide that in fact it is you that is moving.
I find that really sickening, because my eyes believe one thing, and my
inner ear another. Kind of like watching someone else play
Quake
This also happens after a long trip on some gently and regularly rocking vehicle, like a boat on a calm sea or (again) a train.
Contrast this feeling with feeling like you are moving when in fact you should be sitting still, which happens during earthquakes.
Oh, yeah, nitrous oxide will do that to you, too.