In one of Queen Chrysalis' more diabolical plans for the conquest of Equestria, she planned on not only hypotizing the entier poplation of Las Pagasues by taiting the water with a mind contol pathogen, she also planned to turn the Element bearers into changelings agents to lead the assult against Canterlot. While she managed to convert Twilight and bind her to the hive mind, it was the actions of the Doctor who not only broke the Queens hold over her (using his pain and loss to overwealm the hive mind conection), but set up the chain of events that lead to Chrysalis' deafeat.
While Twilight has long since been returned to normal, she still has access to some of the changeling magic she picked up during her brief time as one. Unfortinutly this can sometimes prove a major inconvinience to Twilight as she can accidently abosrb ambient enegry from her friends and become stuck in her changeling form from time to time. How long she is stuck like this can oftern range from afew hours to sevrel days to use up this excess energy, howver she has descovered that while stuck in it, she can do all nighters without any advurse effects.