Ramp Agent reported being inadvertently locked in a baggage pit when the cargo door was closed at the gate. Maintenance performed a pressurization check of the aircraft with the Ramp Agent in the baggage compartment. When aircraft was depressurized Ramp Agent exited without injury.

Narrative

I was in the forward pit looking for a couple of bags that needed to be re tagged. I got a belt loader and opened the pit and got in. I knew [Maintenance was] done with the pressurization test because the Operations said they had run the test and they needed 30 additional minutes to figure out [the] problem. There were no ramp agents plane side because they were waiting inside until they were told to get gate checks and close up [the] flight. I was in the back of pit 3 behind bags and I had found one of the bags I was looking for. I was looking for the other bag and the door closed. I yelled that I was in the pit but no one could hear me. I called out on the radio to the Lead on the flight to tell him I was in the pit. He did not answer. I called the Ramp Agent and asked him to open the door. At about that time I could hear a faint noise and all of the sudden my ears started to hurt like they needed to pop. I then realized that the Mechanics were re-pressurizing the plane again. I called out on the radio. I started to panic and my ears were really starting to hurt worse. I could hear someone trying to open the cargo door but it wouldn't open. I knew there was a way to open the door from the inside so I tried and I couldn't open it. I was really upset and panicking at this point. I wasn't sure if I was going to be ok because the plane was still pressurizing. There was a lot of chatter on [the] radio. I do remember the Operations Agent telling the Ramp Agent that she was talking to Maintenance and they told her to tell the ramp that Maintenance was going to depressurize the plane and not to open the door till they gave the word because it could be dangerous. Once the Maintenance told the Operations that it was clear; the Ramp Agent opened the door. It was so scary. I have never been that scared in my life. It was the unknown of what was happening or could happen.