Maybe get your iron checked out? I have iron issues (overload) and noticed the spike after Covid was really intense. If your 'heaviness' is on the right side it could be liver swelling. All cold/flu will give you a spike like this because your body absorbs all the iron from the cells that died. It throws off your balance of circulating/stored iron for a while. Normal people won't notice it but if you have iron issues you will. But this is just a guess too, I am also not a doctor.