Many thanks for your comments and interest. I suffer from slightly elevated blood pressure with a minimum dose of medication and monitor blood pressure with my own little device. So far GPs have thought my blood pressure OK. Never had a migraine before but as you say could be a possibility. Just hanging out for the neuro appt. Other medical question websites have suggested might be Temporal Lobe Epilepsy. Yes, I'll certainly let you know out outcomes. Many thanks again. I feel less alone when I read these comments.
It *could be* that you had a drop in blood pressure and that is why you saw a black void.
The dancing, flickering things - may be visual migraines - at least, these are possibles.
I can understand freak out - but there could be explanations - I hope you find out that you are well. Let us know when you get tested.