I can totally relate with you sarahblue. I am in the middle of working on my dissertation, and it has been complete agony to keep going. I have dropped it several times on account of my depression dips, but I pick it up again and work. The good thing is that I have all my fieldwork done, so now I need to analyze my data and WRITE!
I hate the feeling of pushing back the date for finishing my work and finally graduating! But, I am trying not to be too hard on myself because I am doing what I can, and I found out the hard way that if I push myself too much to get something finished, I end up in a very bad mental and emotional state when I'm done.
I hope all is going well for you now. It seems that everyone gave great advise! Thank you for sharing!