Stress fracture of the proximal 4th metatarsal. First noticed pain in my foot during the O-ringen sprint - prior to this everything had been just fine. When the pain continued to be present in the last 2 days of O-ringen, getting progressively worse throughout each race, I knew it was serious.
Can only think this was caused by a lot of orienteering in inov8s on harder ground than I am used to... otherwise I am at a loss to explain why it happened.
Don't run in inov8s alone for a month in terrain that's harder than you're used to. That's all I have to say.