Claire, there was a recent thread on here about sleeping patterns that you may find useful;
http://www.theanswerbank.co.uk/Body-and-Soul/Q uestion338125.html
There is also a school of thought which would suggest that we are naturally adapted to punctuated sleep, and is perhaps more common than people realise.
http://circadiana.blogspot.com/2006/03/what-is -natural-sleep-pattern.html
Since the changes are recent, it may just be the effect of the run up and duration of the holiday period.
Personally, I think you may indeed benefit from putting back falling asleep from 10 pm to 11pm as an example, at least to see if that does benefit you at all.
Many things will affect our sleep, from age (tendency to require less sleep as we get older), life and physiological changes (pregnancy, newborns, emotional states) etc.