Sudden change in Greys posture

Question
Our 30-y-o Timneh (female?) is getting over a nasty bout of scab-picking at the base of her tail (healing very well, after a couple of months of treatment the vet was happy and said just to keep an eye on her).
In the last two days however, I've noticed her posture changing - I saw that she was slumped right down on her perch.  Today when I came home she was tipping even further forwards, almost falling off the perch then picking herself up before gradually sagging back down again.
I've had her in my lap for an hour and she's been very quiet, and I just put her down on a flat surface to check her posture - she seems slightly wobbly, and has been sagging right down onto her feet, tipping right forwards to rest on her breastbone and chin with her tail very slightly in the air.  Her body is actually being lifted up as she breathes.  She seems subdued and not terribly sure of her motions.  Her belly feathers are fluffed out, but not her other feathers.
Poo seems normal, and she's eating as usual.  
This is behaviour I've never seen in her before - she's always so bright and alert.  I'm taking her to the vet tomorrow, but she's terrified of him and so will probably hide the problem.  Can you suggest a probable cause for this change in posture?  I'd like to rule out any normal parrotty behaviour (inherited/adopted by CAG and TAG 3 years ago, no experience), and take any emergency action that might be needed.
Many thanks.

Answer
That stance is a mating behavior, my amazon always does it for me especially when I pet her or just stay around her cage, it is a sign of her wanting you to mate with her, she thinks you are her mate. Parrots doing this behavior usually bend forward with their chest down, fluff their feathers, shake a little, shake their rear end and place their butt in the air. They also might cue or make weird noises. Other than this I am not sure what else it could be.
Brittany