Keep thinking people are talking about things you insert into computers to watch films on, when they refer to DVT.

Finally realised they actually mean Deep Vein Thrombosis, the thing that kills you after sitting for too long in a squashed-up aeroplane seat.

So what about being squashed on train seats? I wondered, while squashed on a Thameslink variety, reading that a Sussex insurance company will cover people to sue airlines if they suffer.

Can you get DVT from too much time spent sitting on a train?

I mean, I know it's usually only after very long journeys but these days you could almost have flown to New York in the time it takes to get from Brighton to London.

Was pondering these thoughts and shifting position in seat as much as possible, when I looked up and saw, sitting several DVT-inducing seats away from me, good-looking boyfriend of old friend who have not seen for several years.

Since he was too far away to have the: "Hello what have you been up to? Haven't seen you in ages . . ." type conversation, we simply smiled in mutual recognition.

I was planning to get off at London Bridge and take the northern line to Archway.

Unfortunately, I was on the wrong train and this one didn't stop at London Bridge.

But that didn't stop me from leaping up, waving goodbye and mouthing; "Must catch up sometime . . ." to Andy, knocking several standing commuters off balance and rushing to get off train, at time when it should have reached London Bridge.

It was only when I got to the door that I realised we were not at London Bridge but Tulse, Herne or some other hill and that the next stop would be Blackfriars.

Several people were looking at me, wondering if I was going to make it off the train before the automatic doors closed and there were a few raised eyebrows when, after all the rush and drama of grabbing coat off luggage rack etc, I got to the door and then simply turned round again.

By this time my seat had been taken so had to look for tiny bit of room on rail, which holds up ceiling, to lean against while I worked out where to get off instead.

"I thought you were getting off?" said man, against whom I was now squashed.

Somewhat embarrassed, I decided to cover it with a lie: "No, No," I told him. "Just worried about DVT, thought it was time to get up and stretch my legs."

I told the same lie to Andy when, after half the carriage disembarked at Blackfriars, I ended up standing next to his seat.

"I always get up after an hour's sitting - one can never be too careful." I said, realising that this made me sound a lot weirder than if I'd just admitted that I was a bit dozy this morning and was simply on the wrong train and this one wasn't stopping where I wanted to get off.

"So where do you get off?" he asked.

"Ummm, Kings Cross?" I said, wondering if this was a sensible stop to get off at (it turned out not to be, as the station was evacuated due to an emergency - so I ended up having to walk to Camden).

"Right . . . "said Andy. "Well I'm sure the person who got your seat appreciates your concern about DVT."

As he was getting off at Farringdon, he said: "By the way, I thought DVT only affected people who were really very fit. I could be wrong, perhaps you are right."