Hi susie56
I also had hysteroscopy for lining of 7. something as I recall - although I am on cyclical HRT so my lining will vary. The only cause for concern is if you have had possible bleeding and a thickened lining - and even that is a long way from cancer! Also your lining is barely thickened at 6 mm - but actually it's great that there is a point at which women are checked so that nothing is missed. Far better to go for the odd (hopefully) unnecessary test like this, than the contrary.
As far as I understand it, a thickened lining itself is not even necessarily endometrial hyperplasia - which is the type of thickening that can lead to cancer in a small percentage of cases if left untreated, but bleeding is usally the first sign.
How old are you and when did you last have a period? Some oestrogen continues to be produced even after the last period, so I understand, which can read to growth of the lining. I presume for most women it doesn't continue to grow indefinitely.
I had mine with no anaesthetic but like Kathleen I took the recommended painkillers an hour before the procedure and all was well ( think it was 2 ibuprofen and 2 paracetamol?).
Try not to worry!
Hurdity x