Hyper-evolution

Hyper-evolution is a process of rapid genetic mutation, where an individual's body is changed in a manner paralleling millions of years of natural evolution, but occurring within a matter of hours.

Tom Paris of the USS Voyager experienced hyper-evolution after making a warp 10 flight in 2372. His biochemistry began to change, causing an allergic reaction to water, the breakdown of electrolytes, and the congealing of interstitial fluids. The alveoli in his lungs mutated, resulting in him no longer processing oxygen but instead a nitrogen-acidichloride mixture. Eventually, his cellular membranes deteriorated and his lymphatic system collapsed, leading to his apparent death.

However, Paris awakened shortly after, apparently healthy. The Doctor found that his internal organs were being rearranged, some having been absorbed and others grown anew. There were also rapid transmutations in his nervous system, causing bouts of deranged behavior interspersed by moments of lucidity.

The Doctor believed that Paris' DNA could be forced to revert to its original state if the new genetic material were destroyed with antiprotons from Voyager's warp core. Before the treatment could be completed, Paris broke free of his isotropic restraint and abducted Captain Kathryn Janeway, escaping on another transwarp flight. The Voyager crew found them on an uninhabited planet, having transformed into amphibian-like creatures externally resembling the ancient Earth's Eryops genus, as well as having produced offspring. The Doctor was then able to complete his antiproton treatment and restore them to normal. 

A synthetic version of hyper-evolution, but in reverse, occurred on stardate 47653.2 (2370), when Lieutenant Reginald Barclay was treated for a slight case of the Urodelan flu - the treatment was administered by Doctor Beverly Crusher aboard the USS Enterprise through use of a synthetic T-cell, which became airborne within the starship, mistakenly activating the dormant introns within the DNA of every person aboard and causing a rapid "de-evolution" of almost the entire crew.