Left leg flex-or tendon unresponsive, when seated or standing or walking unable to point toes/foot upwards using muscles/tendons partial loss of sensation in left leg from knee down, causing embarrassing limp, 25 year old male

This. This sounds like a serious issue that should be evaluated in-person by a qualified physician! If your weakness was sudden, there are numerous possible causes, most importantly associated with your nervous system. It does not sound like you had a trauma, so muscle-or-tendon ruptures are unlikely. The most common reason for this problem is an acute disc herniation in the lumbar spine, that can occur without back pain or even any kind of bending/lifting injury. This causes nerve compression that gives patients typically radiating leg pain, numbness and weakness. The muscles that are associated with each lumbar spine level need to be tested individually during a good physical examination, and the distribution of your numbness should be traced. That can often lead to a pretty good diagnosis, even before imaging studies are done. You will probably need a set of standing lumbar x-rays and then possibly an MRI of your back to determine the real cause of the problem. There could be an inflammatory problem with onevof your nerves in the buttock or leg, although that is not as common as nerve root compression in the lower spine. Very rarely can individual nerve roots be affected with a disease inside of the cauda equina, the lower part of your nervous system inside of the lumbar spine, so that is unlikely. Even more rare would be a spinal cord problem higher up in the spine, or some kind of stroke inside of your brain, so that would not be the first thing your doctor will be looking for. Make sure you tell your physician as clear as you can when the problem started, where you feel weak, and where the numbness is (front, side, back of the lower leg?). Associated fever, chills, recent weight loss and problems with urination are important to convey to your doctor also. Do not wait too long to go see someone. Hopefully you can be treated with a course of anti-inflammatory medicines (similar to ibuprofen) and maybe physical therapy to see if things improve. Even with weakness, there is no good evidence for early surgery, as most patients -even if they were weak for a long time from nerve-root compression- eventually regain their strength just fine. Depending on the evaluation and possible MRI scan, do not let yourself get scared into surgery right away; try non-operative treatments first. If things do not improve, and there is indeed a significant amount of nerve compression in the lumbar spine, surgery might be the answer, and it is often very successful for this. Good luck!
Peripheral vs spinal. Sounds like you have a problem with the nerve that controls your lower leg. You need an exam and possibly some imaging to sort out where the problem is.