OP - You've perfectly described the well-known "starvation mode". It's nice to see that you understand what your body is going through.
>> Current Stats: 90% Primal / 143 lbs / ~25% BF
>> Goal (by 1 Jan 2014): 90% Primal / 135-ish pounds / 20-22% BF
>> Upcoming Fitness Feats: Tough Mudder, June 2013
>> Check out my super-exciting journal by clicking these words.
Weight does NOT equal health -- ditch the scale, don't be a slave to it!
Minnesota Starvation Experiment - Wikipedia, the free encyclopedia
1560kcal per day for six months was designed to be "severe and prolonged dietary restriction".
"It's a great life, if you don't weaken.". John Buchan