lob sided disco

Hi can anyone help, my td5 2002 disco has gone very un level when parked on a level surface. The passenger side looks to have lifted up in the air, there is a good 12" clearance from the top of the tyre to the wheel arch. I once had a leaking bag, but that was deflating overnight, this looks opposite it looks like someone has pumped it up. The bag on the back passenger side is fully extended Does anyone know what causes this & how can i fix it.

cheers chris

Could be a hight/level sensor sticking or has gone faulty.