It could also be due to the fact that A) he absorbed a bunch of radiation after freeing Wilf from the glass chamber or B) that he fought the regeneration for so long (visiting Sarah Jane, Rose, and Jack) that it just built and built until he couldn't contain it any longer.
Oh, ok.. Interesting, what will happen with 11th doctor regeneration...
amer007
it was a fact that when ever the doctor regenerates he becomes in a state of loopyness.
Darrell
I can't help but wonder how does the regeneration energy apparently damage the TARDIS? and how did Matt Smith seem to be almost "excited" at the TARDIS being badly damaged and crashing towards the earth? curious thinking behind writing and filming that scene I must say - David will be sorely missed no doubt, but I for one have a great curiosity as how that scene and following series 5 opener will play out later in the year (usually around easter time)