Hi Lara,
There is nothing wrong with you for panicking, it is more common with PhD students than we think. One of my collogues was recently awarded a PhD, she told me one day before the submission, she had a major panic attack and seriously thought about not submitting. Her viva went smooth and got only minor corrections. Some times we judge ourself and our work too hard.
Everyone has a different style for doing productive work, I am a narrow focused person (not sure if it is good or bad), I wrote some of the best sections in my thesis, while sitting in a busy coffee shop. I had my best research ideas while having long walks and looking at trees !!!
Thomas Edison never kept track of time, "I owe my success, to the fact that I never had a clock in my workroom". Sometimes we try hard to become too productive, which is an elusive aim. Average productivity is enough, we need to find a work process that provides good output, aiming for the perfect output, is not realistic.
I agree with tractorgirl, start with easy things every day, like reading/revising a paragraph, it will give you the start you need. I suggest that you focus one a single chapter at a time, a finished chapter is better than 2 not finished. Don't keeping thinking about the 2 weeks deadline, just focus on today and aim for a good working day, tomorrow has not yet come, you will deal with it when it arrives.
Good luck