Rode the recumbent bike at the Y again, 12 miles this time in about 48 minutes. Stretched, did core, then went over to the indoor track. Walked two laps, then decided to try and run a bit. Made about 4 steps and that was it. Too painful on every step.
I'm fairly certain this is achilles tendinitis on my left leg. The achilles itself has felt "thick" or a little hard, and now the pain is gradually moving lower, toward my ankle. I'll shut it down a bit and focus on icing/stretching/rest, see how this goes. Keeping somehat fit will be a priority, since I do still have a plane ticket purchased for Japan. I'll reassess the "best case scenario" in a week or so.