Endolymph is the fluid contained in the membranous labyrinth of the inner ear. For an alternative meaning, see ear (botany). ...
Disruption of the endolymph due to jerky movements (like driving over bumps while riding in a car) can cause motion sickness. Motion sickness is a condition in which the endolymph (the fluid found in the semicircular canals of the inner ears) becomes stirred up, causing confusion between the difference between apparent perceived movement (none or very little), and actual movement. ...
The endolymph produced while under the influence is itself influenced by the specific gravity of the blood when it was made.
The endolymph, however, is a little less dense than usual, reflecting the state of the dilute blood when it was made.
So now the cupula will sink in t he endolymph, and the spinning, although perceived in the opposite direction as before, is back until blood and endolymph again become equilibrated to their normal specific gravity.