Hello,
Thanks everyone for taking the time to reply and give me some encouragement. I liked the reminders that the state of my head is really no one else's business. I was bullied as a kid because of my appearance and ever since then I've somehow assumed people will be unkind if I look different - although deep down I quite like being unconventional. Maybe I should try purple hair next time!
And yes, pulling hair is my really unhelpful method of dealing with stress. At the moment I am trying to do too many things in my life, and the pressure is too much. Maybe when I finish the PhD in the summer I'll stop attacking my hair.