@Mistress Dizzy I hope I'm not too late to maybe give you an option to relax. I know how you feel, I'm actually diagnosed with Generalized Anxiety Disorder and have had a few panic attacks (not fun). I honestly find exercise helpful, it makes me focus on one specific thing and I physically work out the tension in my body from being anxious. I find reading to help or sometimes i'll toss a movie in/turn the T.V. on and knit for a while.
If i'm really having a bad day with it i'll take 5-10min to lay down and kind of meditate. I can't turn my brain off either, also with being a girl we don't really have a special 'nothing box/space' to visit. What I do is i'll lay down (if i can in that moment) and have my arms comefortably at my side. I then try to take deep breaths and i mean deep (initial filling, chest inflates, stomach inflates), and focus on feeling the breath in my body. Kinda like imagining yourself as a balloon, felling the air/warmpth fill your arms into your fingers and back out. I just spend the time doing that and it usually helps.
I hope something helps you out of all the things suggested :s