This is an old post, so I'm not sure you will see my reply or if you are even still visiting the forum.
Did you end up taking Xanax? Did it help?
I was on Xanax for about 2.5 months after having a panic attack that gave me 100% insomnia for four days straight.
I've been off of it for 4+ weeks now.
I had some sort of unknown health issue that triggered weeks and weeks of anxiety. The only doc that could help me was my ND. He found that my neurotransmitters were low like Serotonin. So, we started a regiment to help bring those levels up.
After going off Xanax, I was still having anxiety, then after 3 weeks the anxiety began to increase to the point of panic attack at times. This is a withdrawal symptom, but at the same time I think some of it may have been was rebound anxiety from my previous health condition.
In any case, I think I experienced a similar feeling that seemed to be just switched on all of a sudden in my head. It actually went along with a strange pressure/headache that was in the top back right side of my head. It made me feel very nervous, scared, hopeless maybe, a feeling I've never felt before in my life. It went away, but then came back weeks later, and lasted a couple of weeks. It seemed to be triggered when I ate, then lasted most of the day, then tapered some in the evenings. Then it went away again. Weeks later it's back, since last Monday. But, this time it's a bit stronger and the fear it gives me is even more tense at times especially if I think about it too much.
When I look back, this feeling seemed to be triggered during a time of high anxiety/stress. So, my thought is that it might be a pre-panic like feeling without the panic attack. Or, it could be depression due to the anxiety. I'm not sure.
The good news is that the feeling tends to go away. I think I've noticed when I got a good night sleep, I'd feel better the next day. I've also been struggling with insomnia for a couple of months. Anyway, when the anxiety is low, and I feel physically good, and that strange feeling is gone, I feel normal, happy and ready to enjoy life. And I don't easily think about that scary feeling I had before, almost like it never happened.