As anyone in the equine industry can attest, horses can kill themselves in a padded cell!

Case #1 - Ambrosio, my one month old colt, punctured his eye last week on, I don't know what. He's now been in the horsey hospital, with mom, for 8 days with a bacterial infection in that eye. The doctor's believe he'll make a good recovery with possibly a small blind spot in that eye; he'll be in the hospital for at least another week. $$$$$$

Case #2 - Belleza, my white mare, is having another bout of tying up; basically the horses muscles are overworked and aren't getting enough oxygen. She hasn't been ridden in a few months so I can only assume that she got worked up after I trailered Ambrosio and his mom, Isabella, to the equine hospital. More $$$$
I'm splitting my time between visiting the foal and mom at the hospital and administering shots, here at the ranch, to Belleza. In between I'm finding that doing some artwork is helping keep my mind busy, hence the 3 photomanips in the past 4 days. At least that's free!
Honestly, I don't much about horse health...but is it possible that your mare's muscles are seized up because she's not moving around a lot? Is she just stiff, or is it something else? Sorry for seeming nosy, I love horses...and I hate I know so little about the health care of them...so I try to ask where I can...
We got really the other day...we were fitting tack to our mini..and something was really bugging him when I took him for a test drive...He kept switching his tail and doing little bunny hops. We adjusted things a little and tried getting him moving forward again...It is most unnatural to see a horse attempt a backflip...he landed sideways between the cart poles...thankfully the worse we got were a few bruises for us two footers and a scraped lip on his part. Horsefeathers I thought he was going to break a leg...though he wasn't thrashing a lot.
In general, the horse exhibits stiffness and a reluctance to move forward. Also, if you suspect a horse is tying up, make sure you call your vet immediately (tying up can be fatal - like everything else with horses), keep the horse hydrated and restrict dietary sugars (grain, treats, electrolytes with too much sugar, certain hays).
This is just my advice and should not replace the advice of your veterinarian.
I just returned from the equine hospital and the baby's eye is getting better.