I seriously doubt you have a hyper extended knee. You would have to be in a serious cycling accident for that to happen. There is practically zero chance of it happening during normal riding.

Hyper extending your knee means you extend it beyond its normal range such as by twisting it past its normal range or bending it back on itself. If you should ever do that, the results are usually torn tendons, ligaments and/or muscles. Athletes that do such a thing are usually curled up in a fetal position on the ground in intense pain. They certainly cannot ride a bicycle for another 50 miles.

You more likely have sore ham strings. Ham strings get used a lot during clipped in riding. They are not used that much during walking and running so they get sore. I find that the faster I spin, the more sore they are the next day. Do some stretches, put heat and ice on it, and give it a rest to recover. Like all muscles, they will get stronger with use so they will be less sore after the next ride.