The Doctor's regenerations
The Fifth Doctor recuperates from his regeneration in the Zero Room (from Castrovalva, 1982). As noted, the Doctor frequently experiences a period of physical and mental instability following regeneration and some post-regeneration experiences have been more difficult than others. The Fifth Doctor (in Castrovalva) begins reverting to his previous personalities and the Sixth Doctor experiences extreme paranoia, flying into a murderous rage and nearly killing his companion (The Twin Dilemma, 1984). The Eighth Doctor experienced amnesia as a result of post-regeneration trauma (the 1996 television film); uniquely, the Doctor was "not alive" at the time of this regeneration. The regeneration from the Ninth to the Tenth Doctor sees the Doctor unconscious for most of the next fifteen hours ("The Christmas Invasion"). In the series four finale of the revived series, "Journey's End", an injured Tenth Doctormanages to avert a full regeneration by channelling "excess regenerative energy" into his severed hand, allowing him to heal without changing form. The limb ends up developing into a half-human clone when Donna Noble touches it; the event, a "two-way" "Human-Time Lord Meta-Crisis", also gives Donna a Time Lord's mind. The Tenth Doctor learns of his impending demise in "Planet of the Dead"; in The End of Time, he laments that even if he survives using regeneration, the death of his current personality and attributes makes for something much akin to an actual death. His last words were "I don't want to go." As mentioned previously, in "The Impossible Astronaut" a future Eleventh Doctor is shot twice and begins to regenerate, but is shot again and apparently killed before the process completes.
The TARDIS appears to assist in the regenerative process, as suggested by the second Doctor's statement to this effect shortly after regenerating from the First. This is reiterated by Jack Harkness' insistence that the Doctor be taken into the TARDIS having been shot by a Dalek in The Stolen Earth. Of the five occasions on which he has regenerated outside the TARDIS, one is forced on him by the Time Lords (Second to Third Doctor, The War Games), one requires a Time Lord to give the Doctor's cells a "little push" to start the process (Third to Fourth, Planet of the Spiders), one needs the TARDIS's "Zero Room", a chamber sealed from all outside forces, to help him recover (Fourth to Fifth, Castrovalva) one occurs a few hours after he has actually "died" (Seventh to Eighth, the 1996 television film) and the last he is killed before fully regenerating (Future Eleventh, The Impossible Astronaut). The Seventh to Eighth regeneration remains the only one that takes place significantly far away from the TARDIS, without any obvious interaction from other Time Lords and resulted in the Doctor suffering near-complete amnesia for nearly a day until an event inside the TARDIS triggers his memories to return. The future Eleventh Doctor is killed in mid-regeneration, showing he is vulnerable to death while regenerating and as such his need for the TARDIS may be for safety rather than aid. However it is later revealed that this regeneration was indeed a simulation since the Doctor who was shot was actually a Teselecta robot.
The TARDIS appears to assist in the regenerative process, as suggested by the second Doctor's statement to this effect shortly after regenerating from the First. This is reiterated by Jack Harkness' insistence that the Doctor be taken into the TARDIS having been shot by a Dalek in The Stolen Earth. Of the five occasions on which he has regenerated outside the TARDIS, one is forced on him by the Time Lords (Second to Third Doctor, The War Games), one requires a Time Lord to give the Doctor's cells a "little push" to start the process (Third to Fourth, Planet of the Spiders), one needs the TARDIS's "Zero Room", a chamber sealed from all outside forces, to help him recover (Fourth to Fifth, Castrovalva) one occurs a few hours after he has actually "died" (Seventh to Eighth, the 1996 television film) and the last he is killed before fully regenerating (Future Eleventh, The Impossible Astronaut). The Seventh to Eighth regeneration remains the only one that takes place significantly far away from the TARDIS, without any obvious interaction from other Time Lords and resulted in the Doctor suffering near-complete amnesia for nearly a day until an event inside the TARDIS triggers his memories to return. The future Eleventh Doctor is killed in mid-regeneration, showing he is vulnerable to death while regenerating and as such his need for the TARDIS may be for safety rather than aid. However it is later revealed that this regeneration was indeed a simulation since the Doctor who was shot was actually a Teselecta robot.