I am so sorry you didn't make it to your appt...esp because you had all that stress beforehand and then nothing came of it except a bad headache. (Hope your neuro can help you with the migraines if they aren't already.)
And it's perfectly okay you had to reschedule so you can work on your anxiety before going...it's not worth torturing yourself before an appt! I only hope your T can step up to the plate and help you out...what you need and what you get from her generally has me concerned and I will be po'ed if she completely screws this one up.
And good for you for getting out there and talking to a sales person, esp. at Best Buy, one of the most intimidating stores ever!