I have experience with using Seroquel while recovering from a head injury. Overall, if you're simultaneously dealing with anxiety disorders and a TBI, I would stray away from Seroquel. While it helped immensely with sleep, it totally erased much of my personality. I was zombified, in short. I never went above 150 mg's.

As far as I'm aware 600 mg is a dose prescribed, generally, to those suffering from issues like schizoaffective disorder, bipolar psychosis or schizophrenia.

Seroquel is, I don't believe, labeled to treat anxiety disorders. So it's odd he would prescribe Seroquel, and then rail against the use of SSRI's to treat anxiety, when Seroquel's primary use is for the treatment of psychosis.

As others have mentioned, it is an atypical antipsychotic. It is a very strong drug with at times alarming side effects. Doctors sometimes prescribe it off-label for sleep, but I believe this reflects irresponsible prescription practices. But, it is an effective sleep medicine. If anything, I would use it sparingly for sleep, if you have any issues with insomnia or symptoms of that sort.

Try and see if you can find another doctor.