Even though you love doing something, it doesn't mean you're going to be excited or want to do it 100% of the time. When I rode sometimes I didn't feel like going. Most of the time it was because of my social anxiety or lack of confidence as a rider, but after going I would feel much better. Still, sometimes after a ride I would feel horrible, but that happens to everyone. You can't have all days be good days!

I would keep going for a while, and if you're still not wanting to go, you should evaluate your feelings. Is it the trainer? The barn atmosphere? The horse you are riding? Sometimes a trainer or horse just isn't a good fit for what you need. It took me YEARS (I'm talking like 10+ years) to find a trainer that I worked well with. Now I have two trainers that I know I could go to when I get back into riding in the future :)