A panic attack was a sudden surge of fear, anxiety and panic felt by an individual. One of the symptoms is an increased heart rate.
In 2373, Lon Suder suffered from a panic attack after killing a Kazon, which The Doctor tried to help him through. Suder had a panic attack because he had tried for months to suppress his murderous tendencies with meditation from Tuvok. (VOY: "Basics, Part II")
Later that year, Lieutenant Tuvok had what appeared to be a nervous breakdown on the bridge of the USS Voyager. After scanning him in sickbay, The Doctor told him that if he were Human, he would have had suffered from a severe panic attack. (VOY: "Flashback")
In 2375, Neelix had a panic attack in the middle of the night in his quarters, due to his nihiliphobia while Voyager was trapped in the Void. (VOY: "Night")
Later that year, the Talaxian described panic attacks as being a ten on the "Naomi anxiety scale". (VOY: "Once Upon a Time")