Given a few base assumptions, and using PV=nRT the most likely scenario is minor to major bends, maybe ruptured ear drums and things from rapid pressure drop.

The subject chamber couldn't develop a full vacuum, but a ratio of chamber to plunger volume. The volume would change the temp would drop a little and the pressure would drop a lot. Reverse it and pressure and temp go up. But if the pressure drop was high enough the nitrogen in solution in ylur blood would come out but the pressure rise again wouldn't be enough to make go back in solution.

The bends are painful and starts in places like the joints but can mean death if severe enough.