Exit the submarine without putting on the pressure suit.
You figure out how to exit the ship and proceed to leave the safety of your borrowed craft.
Unfortunately, since your body cannot withstand the immense pressure of this depth, you promptly implode as the hatch is opened. Your body parts splatter the inside of the exit hatch, but the swamp water quickly washes it all away. Your remains drift to the bottom, to be devoured by the small deep-depth bottom-dwellers and scavengers of the swamp.
You're a smart one I'll tell you that. Leaving an underwater craft that is pressure-sealed, to swim around in depths that cause quite a few thousand pounds of pressure per square inch, and expecting to survive! Yep, Roger, a true genius.
After you go through the door from the sub bay go left and get caught by the aliens.
The alien grabs you. It looks like you're in for trouble now.
Well, having captured you the aliens have taken you to a dark room and strapped you into some strange contraption. You can only wonder what they have in store for you.
Energy starts coursing through the strange clamps attached to your head.
A powerful energy was just slammed through your brain. Your brain bounced around inside your skull for a second before imploding into mush.
Your last thought was of latex and babes, not necessarily in that order. You die quickly but the sight of your brain oozing out of your ears might have been upsetting so perhaps that was a good thing.