A concussion was a common head injury characterized by a loss of humanoid brain function as a result of a trauma. One of the symptoms was ringing in the ears. (TNG: "Parallels")
In 2152, Commander Charles Tucker III suffered a mild concussion when Shuttlepod 1 was damaged during the destruction of Paraagan II, but Doctor Phlox believed that he would be fine. (ENT: "Shockwave")
That same year, Ensign Hoshi Sato suffered a severe concussion when Enterprise NX-01 was struck by a Romulan orbital mine. She eventually made a complete recovery, but was eager to return to her post, even before Phlox had finished treating her. (ENT: "Minefield")
In 2153, Captain Jonathan Archer suffered a concussion after being struck by a spatial anomaly but made a complete recovery. (ENT: "Twilight")
In 2267, Chief Engineer Montgomery Scott was thrown against a bulkhead of the USS Enterprise, causing a concussion for which he needed rest. (TOS: "Wolf in the Fold")
In 2367, Jono was found to have a low-grade concussion, sustained at some point while engaging in the Talarians' rough-and-tumble games. (TNG: "Suddenly Human")
Soon after, Doctor Beverly Crusher found no indication of a concussion to explain the loss of Deanna Troi's empathic abilities. (TNG: "The Loss")
In 2368, Soren suffered a mild concussion when the Magellan suffered an inertial damper failure and she was thrown across the shuttlecraft floor. (TNG: "The Outcast")
In 2369, Tahna Los came aboard Deep Space 9 with a minor concussion after his scout ship was destroyed by the Aldara. (DS9: "Past Prologue")
According to Doctor Julian Bashir, the illusory Jadzia Dax had a "nasty concussion" after she knocked her head on a console. (DS9: "If Wishes Were Horses")
In 2370, Jean-Luc Picard was concerned that Voval might have had a concussion following the crash of the Iyaaran shuttle. (TNG: "Liaisons")
Soon after, Bashir found that Melora Pazlar had suffered no concussion following a fall. (DS9: "Melora")
After shifting into an alternate quantum reality that year, Lieutenant Worf had suffered a concussion after being hit over the head in a Bat'leth competition that he had won in the prime reality. Doctor Crusher recommended vertazine to treat it. (TNG: "Parallels")
In 2371, The Doctor, having just been activated, casually diagnosed an injured USS Voyager crewman as not having a concussion and for him to be cleaned up to resume duty. (VOY: "Caretaker")
Later that year, Tuvok received a concussion following a Komar energy discharge. (VOY: "Cathexis")
Also that year, in a malfunctioning holoprogram, The Doctor visually diagnosed a holographic Kathryn Janeway as having a concussion. (VOY: "Projections")
Soon after, Dax was dealt a severe concussion on the USS Defiant by a Changeling infiltrator. (DS9: "The Adversary")
In 2372, Captain Benjamin Sisko received a concussion when the Defiant came under attack from a Jem'Hadar warship. (DS9: "Starship Down")
Also that year, Keiko O'Brien received a concussion when she was thrown against the bulkhead of the USS Volga. (DS9: "Body Parts")
Soon after, Teirna came aboard Voyager with a concussion among other injuries. (VOY: "Basics, Part I")
In 2373, Arridor and Kol dealt Ensign Murphy a blow that left him with a severe concussion. (VOY: "False Profits")
Later that year, Neelix received a moderate concussion in a plasma explosion. (VOY: "Fair Trade")
Soon after, Neelix was diagnosed with a concussion while trying to aid a Nezu planet being bombarded by asteroids. (VOY: "Rise")
A short while after, Tom Paris suffered a mild concussion when his head struck the side of the Cochrane while trapped in an astral eddy. (VOY: "Real Life")
In 2374, Kellin was beamed aboard Voyager with a minor concussion. (VOY: "Unforgettable")
In 2375, Paris told Samantha Wildman she had a minor concussion following the crash of the Delta Flyer, though he was understating the extent of her injuries. (VOY: "Once Upon a Time")
In 2376, B'Elanna Torres suffered a mild concussion in a vision she experienced following a near-death experience. (VOY: "Barge of the Dead")
Later that year, Chakotay was dealt a severe concussion aboard the Flyer due to shock waves from a dark matter asteroid colliding with a graviton ellipse. (VOY: "One Small Step")
In 2378, while playing the role of the EMH in The Doctor's holonovel Photons Be Free, Paris treated Lieutenant Marseilles' concussion. (VOY: "Author, Author")
Later that year, Paris was concerned that Joe Carey might have a concussion after being assaulted by the natives on an unidentified planet, but was prevented by Brin from treating him with equipment from his medkit. (VOY: "Friendship One")
In 2381, Paris, while on a handshake tour at the USS Cerritos, assaulted Ensign Brad Boimler after mistaking him for a Kazon. After meeting up with his fellow Ensigns in the brig, Boimler mistook a wall with a seam on it for a malfunctioning door. When Ensign D'Vana Tendi pointed it out, Boimler laughed it off and nonchalantly mentioned that he might have a concussion as he left. (LD: "We'll Always Have Tom Paris")