My Husband Has Been Suffering With A Very High Temperature

My husband has been suffering with a very high temperature for the last 3 days, this gets progressively worse in the evenings. He also has headache, aching joints and keeps belching. At first he thought it was heat-stroke/sun-stroke, but I would have expected to see some improvements by now ... and why the constant belching? He also has had a touch of diarrhea and has only managed to eat one banana since Sunday.