The vagus nerve is powerful, and a tight dive suit can set it off

Dear Doctor Roach: I’m a scuba diver, and I recently purchased a dry suit that is expectedly tight on my neck. During my first dive with it, I pulled the hood down, and within a few minutes, I immediately felt nauseous before even entering the water. I also briefly felt lightheaded and faint. I removed the hood, loosened the neck a bit, and tried to relax. The feeling somewhat subsided.