if you fly during attack of cold or upper respiratory tract infection there is high chance that tube connecting your nose and ear will fail to equalise air pressure in the ear. in high altitude this tube is very important because of pressure variation in atmosphere. when it fails to function there will be severe negative middle ear pressure or vaccum which may some time lead to bleeding into middle ear known as hemotympanum. this condition is self resolving. kindly consult nearby ENT specialist to be sure about the diagnosis