I did a little research based on the suggestions I got here, and thankfully I don't think my symptoms are consistent with plantar fasciitis. I have read threads posted by the ladies dealing with that and it sounds so painful and frustrating.

It seems likely that I just strained the achilles tendon a bit, as the discomfort is right where - according to the medical illustrations I found - the tendon connects to the calcanus (heelbone). It is feeling somewhat better today so I will ice it a bit and take some anti-inflammatory meds, then see how it does after a mild bike ride today.

If it's not continuing to improve tomorrow then I'll head to the doc's, but so far it seems to be slowly resolving. Thanks for all the input, I really appreciate it!