It took a few minutes, but eventually I realized the grogginess and headache were symptoms of carbon monoxide overdose. I shut off the heater (a catalytic with very low co emissions) and opened the door. It was two days before I could think clearly again. (How could I tell, you ask?)
I had the windows cracked enough, I thought, but there was no breeze and the monoxide, heavier than oxygen, accumulated below the window openings. After giving it some thought I realized she started the leaping when I started using the heater. She hasn't done it since.
A heroic cat!
No, she didn't lose her tail. I can only surmise that in the above photo she was, perhaps, striking a Napoleonic pose.