Probably going scuba diving. Me and my buddies thought it was gonna be ~super fun!~ but after we descended, the horrible ear pain, not being able to see the ocean floor but only the dark abyss I had a panic attack. I started hyperventilating while flailing around as my mask filled with water. Thankfully we were pretty close to the surface and one of the instructors took helped me ascent quickly. I sat on the boat shaking petrified thinking what would have happened if I was underwater and couldn't resurface quick enough. I realized how much I feared the ocean.