I think the first thing you need to do is stop driving, (till your sorted) tell your "passengers" they have to find alternative arrangements, it will be the acid test for you fiance too... If you are getting into a lather as you say then you really need to seek medical help, there is obviously something going on elsewhere.
Driving is something you should get pleasure from, it isn't helping to be under pressure like you are, the basic rule about speeding is that the limit on UK roads is 30moh. If the limit is altered there are/should be signs uo to inform you of the speed, ie 20, 40 50 etc and then 60 on an open country raod A or B class, it is 70 on dual carriageways and motorways. so long as you use your common sense and stick to the speed limit you should never get a ticket, I haven't in nearly 40 years of driving.
You really do need medical advice, it could be something really simple such as lack of certain vitamins, shortage of Iron for instance can cause all sorts of problems....Your GP will advise.
Hth
Pete