Thanks for your replies. BPII has occurred to me, but I always feel that mine isn't 'extreme' enough to qualify. For example, the 'hyper' states don't last very long at all, and often I don't feel 'elated' as such. With the example I gave before, the racing thoughts were actually highly unpleasant to cope with.
I've only recently been to see a doctor, which was very difficult. He's referred me to Health in Mind for an assessment, which should be coming through any day now. I have looked at their website though and one of the things they can't help with is bipolar - typical! But maybe they can advise...