Ok, I know me replying to this post won't convince you that you don't have a brain tumor, because I suffer from the same fear (amongst others), and even had an MRI. I still think I have one.
But, I can tell you that anxiety can make you feel like you're not yourself. Neck pain is just neck pain. Feeling foggy can definitely be anxiety, or just fatigue. And as for dizziness, well anxiety can certainly cause that, or even sinus/allergy issues.
Another thing... STOP GOOGLING!!! Seriously. That was the worst thing I could have done. You read the symptoms and they stick with you. Try to relax... what you described sounds nothing like a brain tumor, especially since this just started within a week.