My fatigue and emotional symptoms slowly increase in the hours after O, reaching a peak the day after, and than decreasing and decreasing almost completely usually on day 3 . There may be some residual effects of POIS on day 4, 5 or even 6, but only perceived in demanding situations that would have asked for top shape. All this is if I do not take anything before and after O for prevention and treatment ( if I take pre-O what works for me, I am 90% to 100% symptoms-free, and can also eliminate the rest with appropriate supplements. In addition to that, POIS was longer when I was younger, but now is less severe and shorter because I have, through the years, developed a very healthy lifestyle ( very healthy nutrition, lots of water, meditation, yoga, exercise regularly, good sleep, stress management, .....)
When no prevention/treatment, cannot do sports on day 2 - that will cause me to have still more fatigue, dizziness, cold sweat, marked hypotension ( not to mention that I cannot perform at all, too tired, no energy, no stamina, no motivation, and no interest in social interactions as well - just wishing I could stay in my bed, alone, of course) However, doing sports on day 3 will usually accelerate my recovery.