Yeah I have a couple, I have a very spooky stb, that was abused to the extreme including and not excluding other forms of torture, he was suspended from a front end loader and electrocuted... he has many scares, both physical and mental and he also when I got him was suffering from kidney failure.  One of the things we found was that when his phosphorous was low he was more reactive and less stable mentally.  We got him an injectable and a feed suplement that both stopped him from being quite so flighty, and also as an aside he suffered severe tie up due to ill health, but mainly due to extreme nervousness and anxiety.  These horses do well tired, lots of excercize, turn out, and as much one on one time as possible, also they do better as one family horses, we do not allow many people other than us work with Tattoo, and he gets better each day-- including no one else feeds him, or in any other way works with him not even to shoe, as my husband is a farrier that makes the job eaiser for us... also as he is a race horse, we find that each time someone else drives him in races for us he regresses, but as the week goes on he gets better, so my husband is going to go back and is in the process of getting his race licence back so he can drive him... we found with a balance of the right suplements and with keeping the number of people to a minimum (we are also very experienced horse people - I'm 41, and Joe is 57 and we have had horses since we were young children) that Tattoo has improved leaps and bounds.  He is still not entirely trust worthy, but when I think back to what he was and is, I can see that he has come a long, long way, while is is a horse, he has many pony characteristics, he aslo like your horse does not like horses, and is severely agressive and will attack other horses if given the chance.  He does like my stud horse, and acts like a mother to him in many ways, but will even get rough with him on occassion.  I have found that if you take this kind out with another horse that is stable that they will often feed the good vibes off of the stable horse.  We spent 8 months jogging Tattoo behind Che each day, right on Joe's helmet, as he could spook and run away at the drop of a hat if Che was not leading the way.  Tattoo is also strong and crazy enough to get both himself and the driver killed if he is spooked enough, so until we hit this method off, we were in big trouble with him.  It takes two drivers, two carts and of course a sensible horse in the lead, but I would say that this was the one single reason main reason why Tattoo has settled down to the point that he can jogg (with Joe driving as he is strong enough to hold him now that Tattoo's mouth is not made of iron) with no one in front, he also is half way sane to race, and has calmed down in all but the most extreme cases.  We also broke him to ride, and as he is a stb race horse, this is something like you did when you broke him to do something other than what his orriginal job was, this change of job also helped, but did not cure him.  Tattoo was so bad that he ran over me one day, and really if I was anything, person, object, brick wall, he would have done the same... when he is scared, he is dangerous... but thankfully over time the crazy moments have slowed.  I also find these kind of horses do less 'well' in the more windy times, as you know horses don't like the wind much, and when the season gets cold they are 'fresher' and also I find that the rise in fructan in the grass raises their sugar up, and they also are 'fresher', and more apt to loose their minds. 

As far as training goes, I would say that my husbands attitude is best, and has also paid off for Tattoo, no matter what Tattoo does, once the crazy moment is over -- to give you an idea of how crazy-- he has gotten to the road twice-- we are stabled on the outskirts of London ON on a busy road, and once through the paddocks and nearly on the road-- run away on me 5 times, ran over me, and the other day when he couldn't get on the race track right away nearly had a wreak and ended back in the race paddock trying to get through a doorway into the urine stall that is just wide enough for a horse-- with the harness race bike and driver, he has also been on his hind legs on numerous occassions nearly going over on the race track with other drivers, in the past would refuse to go to the gate, and used to run off the track and into whatever happened to be big enough to stop him... -- that is how crazy he can be-- but Joe no matter what he does never lets it bother him, and when the crazy is over it is forgotten about, never carried forward-- and wonders the horse that used to hold on to the mind crazed jitteres for hours after something would go wrong, now can make a mistake, and then chills almost right away.  For instance right after Tattoo lost his mind at the track the other day, Joe turned him back under the tunnel, back on the track and went his rated mile (to get his licence) this would be the equivilant of a top flight dressage horse loosing it, going throught the showground like an idoit, then going back and doing his test flawlessly, it took that much effort for Tattoo to get it together mentally, once an impossible task, now he can do it...

So I would say persevere, and keep on with your supliment idea, go with the flow, and keep finding things to challenge your pony, as this seems to help our runaway nut case a lot