If you doubt that you have POIS or not, you can do these experiments:
Testing physical symptoms (testing muscle weakness):
Abstain for 10 to 14 days. Then go running and measure how long you can run until your muscles get really tired and you have to stop. Then give your muscles rest for a few days.
Now assume that you don't have POIS. Perform an ejaculation (make sure you do it in a relaxed way and you don't get nervous or worried). 1 day after that ejaculation, go for running along the same road that you did the past time. And again measure the distance that you are capable of running.
If the second time the distance was dramatically reduced, then you have POIS. Else you don't have it. You can enjoy your life.
Testing mental symptoms:
Perform an experiment like the above mentioned but with a mental activity like memorizing a text or poem.
I think this experiment is scientific enough to check if you have POIS or not. Any ideas?