Sorry to hear of your accident
Now I have alot of experiences with physios as this is my main treatment and been having physio now for over 15 years (private funding now) and the physio you saw should not have put you into a bracket (High functional) because each day/person differs, as you explain Quote * but I am exhausted. I am in pain on a daily basis, continuously suffering from fibro-fog, having memory problems and my body keeps letting me down*
Fibro does not mean your unable to work or maintain relationships as fibro differes to each and every one of us. Even tho some people can maintain relationships and hold down jobs this does not mean that person is not struggling, you need help just as much as anyone else does.
I think you need to look into exceptance as you say. Except your bad days, except your going to need support to achieve what you want in life. CBT therapy for chronic pain is good to help for techniques in this. It also helps with things like pacing and working out your limitations. This I feel will be very beneficial for you in your situation and you can ask for CBT from your GP they can forward you onto a therapist if you feel it may help you.