Decreasing Score

Score depends on many factors but I had a score decreasing for many turns even though I had +'ve happiness, +'ve GPT and really doing rather nicely.

I've never seen this before BNW, anyone know what variables would cause the score to decrease?

If you loose cities that decreases your score I believe. Perhaps loosing military units decreases your score as well.

Things that are included in the score are :
The number of tiles in your borders (this is the least important factor in victory)
The number of cities in your empire
Your population
The number of techs you possess
The number of "future techs" you possess
The number of Wonders you have constructed (this is the most important factor in determining victory)

Brave New World also included
Number of Policies you've adopted
Number of Great Works you possess
Number of followers (or generally your Religion).

So you're either losing a war without realising or your neighbours are Boudicca and Isabella.