Interesting... the fact its on and off ... I wonder if it suggests early indication of hardware failure with the mouse?
I can't think drivers could be causing this
Do you notice a pattery by any chance? I'm reffering more to scenario's such as:-
Its working fine while you're on the desk...
Then you get up, put the laptop in your bag, travel/walk/drive around, come back, put it on the desk and its not
Anything to suggest slight movement is apparent just prior to the malfunction?
Reason behind this is most laptops I open to repair, the touchpad is connected to the motherboard with a thin ribbon.
On some cases, we're had RMA's because the mouse/trackpad does not work. On opening the laptop, the ribbon is partially out - by this, i mean VERY slightly but enough to not make total contact.
Obviousl, on movement, it sometimes sits in such a place that there is enough contact to work but on movement, it unsits again.
90% of the time, plugging it back in fixes it.
Obviously this would be for Sony to look at and only failing you have exhausted other possibilities such as bad install (would have to restore) or reinstalling drivers as suggested.
Good luck 
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