An office, work and leisure chair and retrofit kit for subliminal motions of the seated person. The chair has a cruciform base (1) with rollers (4), a pneumatic spring-action post (2) with an interface plate (5) for a seat panel (21) and seat pad (19), and a backrest (22). The seat panel is mounted with wobble capability on a pneumatic cushion, which has deformable air chambers (18, 35) connected by connecting hoses (27) and lies on an elastically deformable hollow body (14). The hollow body pumps the air chambers when a person sits down and stands up. A pump hose (12) with a one-way valve leads from the hollow body to compensate for leakage losses. Connecting hoses between the air chambers have valves (31; 75; 89) such that the wobbling distance of the seat panel and the damping of the wobbling motion is variable.