I witnessed an incident like this around 10 years ago. Like Phil described, the girl walked forward as the train arrived into the platform, she pitched forward and nose dived between the train and the platform. Luckily she didn't make it onto the track, but got caught on the frame underneath the train and was dragged along the platform for around 10 metres. Very luckily she survived and wasn't actually too badly injured, which was amazing considering what had happened. It was pretty shocking to witness though!
To this day I still can't work out how she didn't end up on the track in my case though. It was probably helped by her staying stiff while having the spasms. I work the Unit's involved now and sometimes look at them and just think how lucky she was. This incident is also partly why I usually have my head out coming into every station!