What exactly did you do to it? I now know the name of most foot problems since it seems I have them all.
I had some "heel pain" (vague) before the Highlander. I also had a complete lack of fitness going in as my cardiologist had pulled me off nearly all cardio for most of a month while they were investigating my strange EKGs. So, I fell far behind the pack at the Highlander. I then slipped and banged my foot in an undetermined way and also shredded my shoe, leaving a 12cm tear along the arch. Sticks and stones kept creeping in as I tried to run and it just ached. I dropped out at the first control (which was 4.5 km straight line, but I had wandered off-line a good bit while hobbling around and not concentrating). When I got home, I could barely walk and thought I had a stress fracture, but the current diagnosis is a mild case of plantar fasciitis. I'm having a massage therapist look at it today (as part of a regularly scheduled appointment) and she may give me a different suggestion. I am planning to try to run this weekend - but it may be my last running of the fall if things go poorly. (Then again, if I navigate as poorly as I did two weeks ago, I may check for a brain injury.)
So sorry. Much of that sounds familiar, other than the acute injury. I'm sure you'll be doing a lot of swimming then. ;)