A.K.Haart's post on erratic driving HERE reminds me of an incident several years ago, on the M2 near Faversham.
I used to turn off onto the road down into Canterbury on most mornings, and one particular journey was a nightmare! I was going up the slip road, to the roundabout which straddles the M2, and the car in front, a big Volvo, seemed to veer from side to side, and much more than appeared normal. I noticed him get round the roundabout, almost - and he clipped the kerb losing a bit of bodywork in the process. He then drove back down the opposite slip road onto the M2 towards Thanet onto the same road he'd just left!
I had a single chance to follow him, and consider, just as Mr Haart did, what to do next. He got back on the dual carriage-way, and sped off, sometimes in one lane or the next one. I tried to stop people overtaking me, as he was really a serious threat, and I was getting pretty worried as well, so I rang the police (corded car-phone, no hands free), and got through to tell them what was happening, as there was the makings of a nasty pile-up and I was the only witness! We were all travelling at about sixty mph, and I was driving one handed, because of the phone.
After a couple of miles, he went right off the road, hit a lamp post, which fell into the road, luckily missing everyone, and then ran the car into the hedge! The door opened, and he ran off, then RAN BACK! I gave the police the last bit of info and went off to see what was up, as he was seriously in some sort of trouble.
It wasn't drink or drugs, as after seeing him in a pool of perspiration and smelling his breath there sure signs of diabetes everywhere on the poor chap! Some other drivers had stopped, and we got him under some sort of control, and found some sugary sweets to get down his throat, but he then had a fit, so we really had to hold him down. I couldn't find any special ID which diabetics carry, and got someone to run to the nearby Little Chef for some sugary tea, which we tried to get him to take, with not much success. The ambulance arrived, and they got him in the back, while the police sorted out the car.
But the final twist was this...
I went up to the ambulance, for a final thank you to the guys there, and asked how the poor chap was. One of the crew just said, "Oh, he'll be fine, WE'RE GIVING HIM SOME INSULIN"!
Scrobs exploded! "YOU WHAT? It's the LAST thing he needs right now you just can't do that"!
Luckily, the other crew member came back and realised the error his mate had uttered, and confirmed that they wouldn't be doing that of course, he needed the opposite, but it really was a bit of a nightmare scenario to finish up an already dodgy morning...
(Hope you don't mind me interfering with your post Mr H!)