Oh Lisa, I'm so sorry!!! I'm not very familiar with the UK, but assume you exhausted the statutory sick pay. Would you possibly qualify for the Employment and Support Allowance or some equivalent?
I also lost a job due to IIH, so understand your frustration and devastation. I had never had difficulty performing my job or been released from any other employment..it's an awful feeling and I'm sorry you have to deal with it. There is a possibility you could get back to work once you're properly diagnosed and treated, so focus on getting better and don't give up hope! I had other health issues so took me a few years to get back on my feet, but I've been able to maintain fulltime employment since 2005..even with the occasional revision and surgery.
Hopefully Heidi or another member from the UK will be able to provide you with more appropriate suggestions as far as benefits and options..just hang in there and let us know if there's anything more we can do.