Inhaling three times through the nose followed by a long exhale through the nose or mouth can help to eliminate hiccups by hyper-contracting the phrenic nerve over a short period of time.
The Wim Hof method involves breathing, cyclic hyperventilation, and lung full or lung empty breath holds, which increases the risk of shallow water blackout if done in or near water. However, there is a lot of interest in cyclic hyperventilation for extending breath holds.
Practicing cyclic hyperventilation during breath holds allows you to control the release of adrenaline and explore maintaining a calm state of mind and body when your system is flooded with adrenaline, which can help you cope with stressful situations.
The paraphacial nucleus takes over when we experience stress, causing us to breathe in a panicky way. To combat this, it's important to practice controlled, rhythmic breathing, especially when in cold water during deliberate cold exposure exercises.