No cure so you gotta rest. Nose is stuffed so you gotta mouth breathe. Throat is dry from mouth breathing. Dry throat makes it painful to swallow. Pain keeps you from sleeping and recovering. Lack of sleep leads to worse symptoms like piercing headaches. Need to rest to get rid of the headaches. Headache and swallowing is too painful to rest properly. Lack of rest perpetuates headaches, nose congestion, dry throat, painful swallowing.
What is this BS
It answers OP’s question about why they are so miserable from a cold. It could be that it isn’t a cold.
It also means they should isolate longer to not spread the virus, and (IDK what is currently recommended these days) maybe seek antiviral treatments. Plus it can explain lingering symptoms after apparent recovery.
OP never said those symptoms are unusual for him with a cold. I for one get no symptoms from covid other than diarrhea, whilst I get exactly what OP describes from a common cold
They should do that regardless