Welcome to HCM At 20 years having fever is no cause for excess worry,many healthy normal people get fevers, during exposure to viruses,bacteria,stresses ,low immune status etc most common fevers are curable with 5-6 days of treatment and rest here are the cause of common fevers , 1]viral fever:caused by infection with viruses accompanied by body ache and fever and lasts usually for 3-5 days 2]bacterial fever :commonly seen with respiratory infection[throat,chest]and resolves completely with antibiotic treatment for 7 days 3]malaria:commonly of 2 types,p.vivax and p.falciparum,which is again a completely curable condition but will need hospital admision in some cases. 4]urinary tract infection:associated with burning while passing urine and fever also a easily curable condition 5]typhoid fever:more prolonged fever if untreated,blood tests confirm the diagnosis,depending on the severity of illness patient can be treated at home or in hospital. 6]rarer causes of fever due to tuberculosis[t.b.] etc may be more prolonged. blood tests and x rays may be required to confirm diagnosis in some of the above conditions. and since your friend is ok now no cause for worry.