An update

I've been referred to a sports medicine specialist.  No running AT ALL for at least two weeks, until I have my appointment and get further assessment. 

I gather he'll have more of an idea of what testing and/or treatment will be required.  In the meantime, the physio has strapped a disk to the ball of my foot to cause the metatarsals to splay out when my body weight is applied.  I believe this is to reduce any compression or swelling in the area.  It's like walking around with a large flat stone in your shoe, not terribly comfortable.

I hope to keep swimming twice a week and perhaps cycle on the weekend, to keep my fitness up.  I'll take the opportunity to keep up with the strength exercises and weights to keep my body strong.

Trying to stay as positive as I can for now.  Best case scenario - the complete rest sees me healed in two weeks time... we'll see.  I want to get this right so I can run another half marathon (or several) but if this injury/condition rules me out from long distance running then I'll just have to find other challenges to keep me busy :)