I have BPD, PTSD, Depression, Anxiety, Fibromyalgia and Crohns. I am 28 years old. You want to talk about being a 90 year old in a young persons body?
Sorry to sound blunt and crude but to me it sounds like you are either off your meds, or need a change in your meds. As well as more consistent therapy sessions.
Horses are therapy. Its what they do best. The horse world is full of people with mental issues, physical issues and any sort of disability you can imagine. Horses give many of us a reason to keep going. My jumper coach(who is one of the only level 4 jumper coaches in the world) has not been able to sit in a saddle in years because of injuries.
One of my best friends can not ride because her anxiety gets the better of her and she panics when the horse stumbles. Yet she is a groom for a large show barn and loves it. I know others who will just find things to do with mini's or take up equine photography... there are so many ways you can be involved without riding if you don't think being in the saddle is your thing.
Though I suspect you have something else going on and you may need to talk to someone to sort it out.
Chin up, there is so much support out there for you. Something will work out *hugs*