Question: why do you go all funny when you take step back on earth from being in space ?

Columbus Operations answered on 17 Jun 2016:

Joao: Your vestibular system gets confused once you go into microgravity. What your inner ear (usually is what is use for balance) feels and what your eyes see is no longer matching and this can be really disorientating. Many astronauts feel a kind of “sea-sickness” on their first days in space.

But after a while your brain stops taking into account what the inner ear is “saying” and the Astronauts are fine while in Orbit.

Once they come back, the opposite happens, the inner ear, all of the sudden, is feeling gravity again and is sending this information to the brain. It will get confusing again, until the brain adapts.

Also, while is space, you don’t use your legs too much, so you loose a lot of muscle mass in the legs. That doesn’t help when you are trying to walk again.