The seat cushion on my Spacesaver seat is stuck. What should I do?

Sometimes the plunger mechanism of the seat cushion seems like it's no longer working, refusing to allow you to move the seat cushion at all.
This doesn't necessarily mean the plunger is faulty, it may simply be solved by returning the seat back to its upright position using the reclining mechanism.
Once the seat is in its upright position, the plunger should engage and allow you to move the seat cushion as intended.