When on a zero-g plane when the "waitlessness" goes away where do you sit?Simply on the floor...?

Question

or does the floor open and seats show?

Answer 1

Aboard the Boeing used by NASA for zero-g flights, yes...you simply find a place on the floor at the end of each weightless arc. They fly up to 70 such arcs on each flight.

Seats are provided for occupants for takeoff and landing.

Answer 2

The 727 operated by Zero-G is basically a freighter with a section padded and contained for the weightless flights.  For takeoff and landing there are normal seats for the customers,

Answer 3

Such G-Force aircraft’s interior is divided into two zones. The rear area is called the Seating Zone and provides seating and FAA-required passenger provisions (emergency oxygen, escape path lighting, etc.) for up to 35 passengers and crew. The forward section, approximately 90 feet long, is called the Floating Zone. The floor and walls of the Floating Zone are covered with a special FAA-approved 1.5-inch energy absorbing Ensolite padding.

So after the exercise they all go to the rear to sit on these seats like in a normal flight.