Your quote: I am scared. "I keep thinking of things that have happened in the past and realising they were probably part of all this. I’m not sure I can deny it any longer. Also I felt great during my ‘high’ – I was super-productive, loads of energy and loads of plans. Now I am very disappointed to realise that this was ‘illness’ and not me getting better, as I thought at the time. I’m disappointed that I have abandoned all these plans and I feel like I can’t trust what I think or feel any more."

I think it is all in the way you perceive it. You mention above having a lot of energy and being disappointed it was your illness. It was still you! It is still you. As bipolars we have the unique gift to experience such highs and lows many others may never experience. I see the sun go down and remember how it reminds me of a death of a cherished loved one. I see my grandson and teach him philosophy because he holds the future in his hands.
I think if you embrace it, and realize it is a part of how wonderful you are as a human being, you may come to not only accept it, but embrace it. It's not scary, I view it as a gift.