...and the walls came tumbling down

It seems that Castaneda had a similar episode to mine. In The Eagles Gift he writes:

...I had a sense of mild discomfort which I explained away as a dizziness or a sudden loss of breath due to physical exertion.it reached a climax one night when I woke up terrified, unable to breathe. The physician I went to see diagnosed my trouble as hyperventilation, most likely caused by tension...
...I decided to return to Mexico to seek la Gorda's counsel. After I had told her the doctor's diagnosis, she calmly assured me that no illness was involved, that I was finally losing my shields, and that what I was experiencing was the "loss of my human form" and the entrance into a new state of separation from human affairs.
"Don't fight it," she said. "Our natural reaction is to struggle against it. In doing so we dispel it. Let go of your fear and follow the loss of your human form step by step. "