I was bolted with by a terrified youngster (he was running blind) he threw me off and I fractured my spine. Although I was a reasonably experienced horsewoman, working with horses, riding for a living, and I owned my own horse whom I regularly competed, I totally lost my confidence after this.
The worst thing I did was to keep forcing myself back on unkown, difficult and youngster horses. because it was my job and I had a VERY unsupportive boss who basically said "ride or piss off" (and would chuck me on all sorts of potentially dangerous horses without a word of warning or advice but that's another story) I felt unable to admit either to myself or anyone else how nervous I was. I would get tense and terrified on board and the horse would sense this & play up. This vicious circle made the problem worse. Eventually I sold my horse and left that job.
It took me about 2 years to get over the accident and I will never be the rider I once was. However, I can enjoy a good gallop, jump confidently again, and still work with horses, albeit in a quieter job. I also have a spooky sharp pony whom I absolutely worship!
However, I think if I had been able to give myself time after the accident to come to terms with what had happened, and also to get back into riding at my own speed with supportive people around me, I would have recovered my nerve much quicker. My advice to you would be therefore as follows:
don't get yourself a horse yet. Stick to the wonderful one at your riding school that you feel safe on.
Don't be ashamed of how you feel. It is normal and natural. I bet if you talk to your instructor he/she will be understanding. Most instructors have been there.
insist on taking things at your own pace. Keep a diary of your weekly or monthly achievements. That way you can look back and see improvement instead of focusing on how you 'still aren't back to how you used to be'.
get a supportive, understanding instructor who will encourage you without pushing you - or allowing you to over-push yourself.
keep remembering that it is your choice to ride. It is a hobby, something you do for pleasure.
One thing I always do when I feel the nerves kick in is to think "how will I feel about this when I get home if I DONT do it?" If I think I will feel disappointed, I give it a go. If I think i will feel I have made the right decision not to do it today, I won't.
BIG HUGS to you, it is awful and I really feel for you. If you take is slowly, I'm sure you can get over it and find the enjoyment in riding you once had.