Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. Those symptoms you describe can be found in many different settings, are not specific. So they can t be attributed to dehydration unless there is a clear history of him using many fluids without correct replacement. It would be much more likely to be a viral infection which should improve in a couple of days. If symptoms persist then some blood test like blood count, electrolyte panel would help to screen for infections and metabolic alterations. I hope he feels better soon.