Hmmmm, she just seemed a bit dull today, normally she's quite up for things, but today she just seemed like she couldnt be bothered, but she ate her dinner ok and seemed happy enough, just bit lethargic.
It's a common side effect of worming horses with EPSM and of EMS. Your horse may be a low grade sufferer of one of those two conditions, or have a poorly functioning liver, which will also do it.
If she is barefoot expect her to go footie on stones too.
You might do well to get a liver function test done. Don't stress her with hard riding until she is back to normal, the next stage is for her to tie up if her muscles do too much work.
Unfortunately, I think, Pramox is a 13 week active wormer and it may take some time for her to get it out of her system.
If you want more help, check on uknhcp.myfastforum.org, there are plenty of people on there who will tell you what happens and how to support her liver meanwhile.