I am taking 200mg of Seroquel but I take it with so many other things at bedtime that I'm not sure which helps the most. I had some issues with plummeting blood pressure when I was taking 600mg but on 200 going slowly back up to 300mg next week along with, 2 Ambien, 2 Xanax, 3 Phenarazine, 75mg Amitripyline and 125mg Nortriptyline all at bedtime at least knock me out for 4-5 hours but I haven't seen big improvements in my anxiety or PTSD symptoms. ECT treatments everyother week seem to be doing more for my major depressive symptoms.
The Seroquel is horribly expensive, when my insurance was canceled for about 6 weeks I couldn't take it at all because it was $639.00 for a month supply of 60 pills.
I hope things work out for you, like was said before be sure and ask your Psych doc for samples of Seroquel and hopefully he/she will have some available for you.

Take care!