There are several different reasons that someone might feel a rocking sensation when standing still. You could have an ear infection that is messing with your inner ear balance or you could actually have an illness called Balance Disorder.
My theory is the heat causes you to stand properly and the wright keeps you standing with the gravity in the world.
The rocking motion is a way of self-soothing and distraction from the sensation of any kind of inner distress- such as loneliness, sadness, fear, shame, etc.
If the behavior concerns you it should be evaluated by a medical professional. There could be several underlying causes.
Hooligan Causes a Sensation - 1901 was released on: USA: July 1901
Tourettes or autisum
It has nothin to do with standing still... it has everything to do with standing still with your knees locked. That causes over time a reduction in blood pressure leading up a faint. [improvement] The low blood pressure causes the human body to gain the sensation of weakness, causing you to lose consciousness.
Nerve disorder causes pain with no stimuli. This phenomena is seen often when someone loses a limb and still has sensation of feeling like it is there for a while
It caused by change in pressure. When internal air pressure is higher than of surrounding it causes your ears to pop.
a flaming arrow
hmmm... you might want to get to a doctor!
Lasctic acid fermentation
lactate