Unforgiving Waters

You relax, floating on your back. The water is very cold... but luckily, you're wearing a wetsuit. You can't see the shoreline now. When you try to stand up now, you see that you cannot feel the bottom. Luckily, you brought your goggles and snorkel with you, as well as a flashlight. Good ol' paranoid you. You put your goggles on and click your flashlight on, then stick your face into the water. Underwater, all you can see is blackness, even with the flashlight on. Panic swells in your breast. What do you do?