Feel like I am losing it!

Hi everyone, I am new to this website but think I have finally found some comfort and self-help.

Brief description of my history....suffered panic attacks off and on for about 20 years (brought on by the thought of dying....and consequently given me a fear of it). Have managed to control these pre-disposed attacks because I could mamange the physical symptoms.

However, a year ago I began to go through an extremely difficult period which brought on bouts of severe anxiety. Over the past two months these anxieties have lead to panic attacks but without hardly any physical symptoms such as hyperventilating, sweating etc etc and have ALWAYS had an episode of depersonalisation with these attacks.

Anyway, the anxiety got worse, I felt it first thing in the morning in the pit of stomach and would wake up shaking. The anxiety would get worse and then on the way to work (driving), I would end up having a panic attack but it always started with the depersonalisation feeling which would then evolve into the panic. It would happen at work and soon I really felt like I was "losing it" and "completely out of control".
I visited my GP, told him everything and he told me I had an anxiety/panic disorder and put me on valium (3 x daily).
These really began to help because they kept the anxiety away but after I had finished my first course of valium I suffered an extreme anxiety attack and couldnt even drive to work because I thought I would panic on the way.
Back to the GP's I went who gave me another pack of valium but cautioned me how addictive they were and who promptly then referred me to see a psychiatrist (which I happily agreed to).

To make matters worse I have also been referred to a Neurologist for an CT on my brain because lately I have suffering from extreme migraines where the pain has been so unbearable I thought I would die.
Added now to the complication of anxiety and panics about dying, have managed to convinvce myself that I now have a brain tumour....God...things go from bad to worse dont they!....not an ideal situation for a person with a fear of dying and who also has an anxiety/panic disorder to be requested a brain scan (just incase something needs to be investigated!)

Back to the real problem....the depersonalisation/derealisation subject. These are the feeling that are now causing the anxiety and panic. They happen for no apparent reason and can happen anywhere (mostly when I am at work). One minute I am there...the next...somewhere else, although I still know exactly what I am doing and where I am its the feeling of the depersonalisation that makes me panic and the depersonalisation seems to express itself further then. It may only last a couple of minutes but it makes me feel like I am really losing control of everything and its happening almost everyday.

After reading many websites about this condition I didnt actually realise it was a disorder in itself and I now thik that i have a depersonalisation disorder rather than an anxiety disorder from which it has manifested.
I have tried positive thinking, cognitive behaviour therapy (learnt from myself) but it still happens and I cant control it.

Please can anyone help??????????????? I feel as if it is now taking over my life, I am scared of going out incase it happens, scared of it happening at work (my GP wanted to sign me off sick for a month but knew that wouldnt help)....have I got a brain tumour?...am i blowing things way out of proportion???
Oh yea, my GP has also offered to change the valium (because of dependance to anti-depressants) but i feel that these will have no proper effect or help...can anyone tell me if they are on anti-depressants for this disorder and if they do help....and if there is anything I can do for myself in the meantime.

I apologise for the length of this new topic but feel that the only people who will understand what I am going through...is people who are dealing with the disorder themselves.

Please help...I feel like I am going mad!