It is the late Dr Marcel Waldinger who have coined the name POIS ( Post-Orgasmic Illness Syndrome).
( Dr Marcel Waldinger was the Dutch Doctor who was the first to study POIS )
Dr Waldinger was also the one who defined 5 preliminary diagnostic criteria for POIS :
Criterion 1. One or more of the following symptoms: sensation of a flu-like state, extreme fatigue or exhaustion, weakness of musculature, experiences of feverishness or perspiration, mood disturbances and/or irritability, memory difficulties, concentration problems, incoherent speech, congestion of nose or watery nose, itching eyes
Criterion 2. All symptoms occur immediately (e.g., seconds), soon (e.g., minutes), or within a few hours after ejaculation that is initiated by coitus, and/or masturbation, and/or spontaneously (e.g., during sleep)
Criterion 3. Symptoms occur always or nearly always, e.g., in more than 90% of ejaculation events
Criterion 4. Most of these symptoms last for about 2 to 7 days;
Criterion 5. The symptoms disappear spontaneously.
Dr Waldinger have admitted that the presentation of POIS is variable, but quite well represented by these five criteria.
Reference :
Waldinger, M. D. (2016). Post orgasmic illness syndrome (POIS).
Translational andrology and urology, 5(4), 602.
These criteria may help you to figure out if you have POIS or not, but do not take them as absolute. For example, criterion #4 says that most symptoms last for about 2 to 7 days. It is true for most members of poiscenter, but some members may have symptoms that last for 10 days, 14 days, or even longer. Also, note the the "spontaneously" of criterion #5 means that the symptoms will slowly disappear over time, without treatment.
Do not hesitate to post questions on the forum if these criteria do not make it clear enough for you.
The symptoms mentioned by Dr Waldinger in the first criterion make for a limited POIS symptoms list. You can find a more complete listing of POIS symptoms here on the forum, at
https://poiscenter.com/forums/index.php?topic=3651.msg38477#msg38477 
