Thursday while I was at work it started getting worse. I shifted all my weight onto my right foot and limped a bit, and when I got home I wrapped it up in an Ace bandage and elevated it for the rest of the night. As long as I wasn't standing on it, it felt fine.
Then I woke up this morning, and from the very first step I knew I would have to see a doctor. It had changed from a dull ache to a STABBING! PAIN! every time I stepped on it. I planned on getting to work, getting everything done as quickly as I could, then going into InstaCare to get it looked at. Work wasn't so bad. I was pretty busy, so I was standing and walking all day, but I could rest my weight on my right foot and the left wouldn't hurt so much (unfortunately, this meant my right foot started to ache...), and I limped around until everything was all set up to run by itself. I asked my boss to report my results when they were finished, and he's super nice so he said he would, and I headed over to see the doctor.
Fortunately, the doctor on call was a sports medicine doctor that I had seen before. I had thought initially that maybe it was a sprain, and then later when the pain was sharper I thought it might be a stress fracture (I had had one like six years ago and it felt remarkably similar), but it turns out I have Bursitis. Basically, there's a little sac in between the Achilles tendon and the bones in the heel of the foot, and mine got inflamed. The doctor thinks it's because I started exercising too aggressively, with the incline on the treadmill too high. Oops. I suppose over enthusiasm can be a bad thing...
So, I'm supposed to ice it, do stretches, take naproxen, and stay off it for a few days, then be more conservative with my treadmilling. Sad. Really pumping up the incline was what was really increasing my heart rate and making me burn more calories. I'll have to work on going faster to make up for it (or maybe I'll be bad and work the incline back in, gradually so as not to injure myself again...)!