Hyperventilation was the condition of rapid respiration caused by anxiety or panic.
In 2371, The Doctor tried to calm down a hyperventilating Neelix while the latter was using holographic lungs to breathe. (VOY: "Phage")
Later that year, to explain his presence at Kes' surprise birthday party, The Doctor told her that surprises could cause, among other things, acute hyperventilation. (VOY: "Twisted")
In 2374, The Doctor told a suffocating Harry Kim and Tom Paris to breathe slowly lest they hyperventilate. (VOY: "Demon")
In 2375, The Doctor gave Neelix a mild sedative to control his urge to hyperventilate while the Talaxian recovered from his nihiliphobia-induced panic attack. (VOY: "Night")
In 2376, when Neelix told Tuvok that just thinking about the fate of the crew of the Salvoxia made him short of breath, the Vulcan suggested that he think more pleasant thought to avoid hyperventilating. (VOY: "The Haunting of Deck Twelve")