Thanks for the replies... Blood clots...yikes! I don't have any of the redness, swollen veins, etc. nor any of the predisposition factors that I'm seeing online when I search for that...but thanks for the warning regardless.

I had a consultation with Dr. Google...my best guess right now is either that I have some kind of deep pulled calf muscle, or that maybe it is the upper end of my achilles tendon that got strained. I'm not sure how to tell.

Jesvetmed, I will definitely use the ice & stretching; seems like that would be good regardless of the source of the pain. I tried the self-deep-massage using my other kneecap (great tip btw!) and it doesn't feel that tender, but I'll keep doing it anyway until I can get in to see my PT.

Today it doesn't feel like a very bad injury; the only thing I can do right now that aggravates it is trying to stand tip-toed. I'm just worried about getting back on the bike next week, getting halfway through the ride, and feeling the stabbing sensation again, since I have no idea what I might be doing to have strained it in the first place. My cleats don't appear to be moved, nor seat height or anything like that either. If it was a pedaling technique issue I'd assume it would hurt a little on both sides.

Thanks again for your help!