Head down?

[RhndLev@cs.com]

Hey Ti, Heidi and other lameness experts:

As I said, I'm trying to bring my TWH mare back from an injury.  Our first 
ride, she just wanted to fly.  In subsequent rides, she's settled down a lot. 
 But yesterday, she walked along with her head really low.  Not sniffing the 
ground or stretching -- just holding it really low like a western pleasure 
quarter horse -- below the withers.  Generally, in order to gait, these 
horses need their heads up.  When I asked her to raise her head and for the 
gait, she would raise her head on command, but then lower it and throw it 
back up and lurch into a trot and then lower her head again.  The trot was 
even and sound once she was in it, BTW.  After about a mile and half, she 
seemed to warm up out of it and gaited just fine with her head where it 
always it.  She was fine for a mile and then the head went way down again.

She's never done this before in response to being tired.  My TWH gelding 
would hold his head this low only when he was in pain, but then the low head 
carriage was combined with a head bob toward the opposite side from the leg 
where the pain was.  Special had no head bob at the trot.  She always has 
head bob at the walk and the gait, but the head bob remained completely 
symetrical during this ride.  I can't see or feel any lameness and I trotted 
her out for a friend who didn't see anything (and he's really good at seeing 
lameness).  Any ideas?  Should I stop riding her?  

Rhonda and Special