Assuming it's got a gas lift it looks as if the things sprung a leak. I've never seen anybody fix a faulty gas lift mechanism it's always been swap out busted for new. Depends on the chair whether a fix is going to be economical or not.
Another fault I've seen that had a similar effect was a split in the 5 star base plate where the gas lift mast fitted. The weight of the user slowly wedged the crack open and pushed the centre stem through the base until it hit the floor.