First of all, I want to say I hope you have a good sleep, as sometimes that in and of itself can help tremendously by simply giving you a break. Also, the emotions you are experiencing are very normal. A lot of people liken the response to a diagnosis like MS to dealing with a death, with all those stages of grief one goes through when faced with a death. Just know that it is okay to be angry and sad, but you will get through this.
I am not sure what my official dx is at this point, CIS or MS, so please take the rest of this post for what it’s worth. I met a woman who has had MS for almost as long as I’ve been alive. At the time I “had” MS and was struggling to continue working, had just started Copaxone, and was basically a big mess. I was having a lot of trouble with that unpredictability with symptoms that you mention above. I have a lesion in my cerebellum which causes balance and vertigo issues among other things. Even after the initial flare calmed down, the residuals would get worse in ways that made it quite hard to work, drive etc.
The one time I met this woman in person was at a dinner. I was already feeling pretty lousy, but went went anyhow, and didn't tell anyone when I started to feel even worse. I sat there and got dizzier and dizzier, but I just took a deep breath and thought, oh, it will get better. By the time it got so bad I knew I had to do something, things were spinning so badly I couldn’t tell up from down. At that point I was stuck in a restaurant with a tableful of horrified dinner guests, and we all sat there long after dinner because I couldn’t move.
I talked to the woman later, and she told me to give myself some time, and I would learn to cope with this better. She said that in the beginning, the body is freaking out and doesn’t know how to deal with all the new issues. However, over time, I would learn to adapt. She also said I would learn to read the cues my body was giving me, and stop before I overdid or got into too much trouble. I was kind of doubtful, but she was right.
I am now often able to pick up cues which warn me when these symptoms are going to get worse. Now I try to act right away by taking anti-nausea meds, saying I need to leave if I am out, lying down or getting my head against a solid wall so I can tell I am really not spinning, etc. I’ve also found ways to make things easier on a day to day basis, such as touching walls, looking down etc. I also know that certain things will aggravate the residual issues I have, such as heat, long periods of insomnia, fatigue, stress etc, and that while I am not a morning person, I am most able to function in the morning before the fatigue kicks in.
The point of this long middle of the night ramble is to say that you, too, will begin to pick up on your body’s cues, notice warning signs, and learn methods of adapting. You may or may not be able to enjoy horses and art in the exact same ways as before. However, that certainly doesn’t mean that you should give up on your passions! You can find ways to do both of these activities in fulfilling manners, even if they are in somewhat different ways than what you did before. I was a painter as well, and my dominant arm and hand have been affected. I now express my artistic side through my garden and photography, although I would like to try painting again sometime as well, even though I know my paintings will be quite different.
Also, keep in mind that while the damage has been done and you might always have residual symptoms, it can take many many months, sometimes even years for the issues to decrease down to your new baseline. You are very newly diagnosed and new to these issues, and while other things will most likely crop up at some point, the issues you have now may very well still get better over time, with your PT, and as you learn ways to adapt.
In the meantime, go easy on yourself, hang out with your critters, and keep on posting. We're here for you, and I’m sure others will be along with additional perspective and suggestions for you as well.