At first I thought it was just the summer heat or something. We all get a little sluggish when it's warm out... but it seems to have continued on into the winter. It's had a negative effect on our riding because try as I might, I can't seem to create enough "drive" and impulsion to be able to do anything useful. Now I'm almost happy when she does spook, because for maybe a minute or two afterwards she feels like the horse I knew... but eventually all of that energy peters back out and we're back to plodding around.
She'll be 17 years old soon... is she getting to the age that she's supposed to be slowing down like this? She does seem to have gotten much calmer with the onset of this lethargy... she feels more like a long-rein lesson pony and less like a dressage diva. We've talked to our instructor, the barn staff who work with her periodically, and even mentioned it to the vet when he came out for a routine check. No one seems to have an explanation for it beyond getting older.