(covers information from several alternate timelines)
A subspace inversion is an energetic phenomenon which can produce powerful gravimetric fields. The Bajoran wormhole was known to produce subspace inversions which occurred naturally every fifty years, or which could be brought on when the wormhole was exposed to certain energy emissions.
In 2371, the wormhole experienced a subspace inversion when exposed to a carrier wave in the theta-band frequency, which caused its gravity well to increase by a factor of three. It was later determined that the accident had been caused by Dejar, an agent of the Cardassian Obsidian Order, who was posing as a scientist while attempting to sabotage the deployment of a communications relay in the Gamma Quadrant. (DS9: "Destiny")
The next year, the USS Defiant traveled to the Gamma Quadrant to observe the wormhole experience a natural subspace inversion. When the Defiant was exposed to the increased gravimetric field, however, it caused a power surge in the ship's warp core. Although Captain Sisko was able to shunt the excess power to the Defiant's main deflector, he was hit by an energy discharge which pulled him into subspace, causing him to periodically travel into the future. The timeline in which these events occurred was negated seventy-eight years later, when Jake Sisko, to whom his father was connected via subspace link due to their close proximity during the initial energy discharge, committed suicide. This had the effect of severing the subspace link between the two of them, returning Captain Sisko to the moment of the accident, where he was able to change history by dodging the energy discharge. (DS9: "The Visitor")
While having dinner with Chakotay on evening in 2377, Kathryn Janeway shared "forget particle fountains and subspace inversions. There isn't an anomaly scarier than a thunderstorm on the plains, especially when you're six years old." (VOY: "Shattered")