PT Question -- I'm a little scared about this

[VeloVT]

This afternoon I went for a run, for the first time in about a month. I'm generally out of shape right now, I had a stressful summer with some unfinished school work.

I ran 5 miles, didn't ever feel like I was pushing too hard, legs weren't too fatigued by the end (and not too sore now, three hours later) but at the end, my boyfriend and I always try to pick up the pace significantly for about the last 400 meters. When we are in shape, this becomes an all-out sprint to the death; when we (or one of us, ahem) are not in shape or are not feeling good, it's a good little pick up. Well, I was totally feeling up for it today and we started picking up, and got up to a near-sprint, and all of the sudden, I lost leverage in my right foot/ankle. It didn't go numb, it didn't hurt, I didn't feel or hear anything snap, and oddly, it didn't buckle, although it sort of felt like it should have. I just suddenly couldn't push off with that foot -- the foot was just kind of hanging there and hitting the ground each stride. I was able to keep running until the "stopping mark" probably 100 meters later. During our cool down walk, again, I could walk, and my foot had normal sensation -- heat, texture, weight, etc, wasn't numb, didn't feel like it had fallen asleep, but wasn't "right" either.

Now, several hours later, still able to walk, still normal sensations in the foot, but I can't flex it fully. I can point fully, but compared to my other foot, the most I can flex is probably 80% of normal. If I try to do the exercise where you start with your foot pointed, then pull your foot back as far as you can with the toes still pointed, unpointing the toes last of all, the whole thing totally falls apart, toes completely unable to do anything, just shy of vertical (I can normally get well past vertical, and can now with the other foot). I can do many things more or less normally, I have feeling in the foot, but some parts of it almost seem partly paralyzed.

I don't know if this is related, but I also noticed that, in addition to overally calf tightness, I have a big knot in that calf, slightly less than halfway up, in the back, but definitely to the outside of the centerline. I can feel this when my leg is relaxed, and I can feel it with my hands if I palpate it somewhat deeply (with thumbs). Also a prounounced tightness at the top of that hamstring (and not on the other leg).

During the run, nothing strange happened -- no bad footfall, no twisted ankles, etc...

It's strange that my foot isn't really working, but it's not painful at all, nor is it numb or lacking sensation.

Any idea what this could be? Anything I can do to help it along? Stretching, RICE, etc? Does it sound serious? Should I see a doctor? It's strange and unlike anything that's ever happened to me before.

Thanks!!!