NEW : Obama calls Petraeus from Air Force One . Spokesman says Petraeus fainted , `` is feeling much better '' and will be back in the U.S. shortly. Petraeus was set to testify at Senate Armed Services Committee hearing .
NEW : Obama calls Petraeus from Air Force One . Spokesman says Petraeus fainted , `` is feeling much better '' General says he got `` a little dehydrated , '' had n't eaten breakfast . Petraeus was set to testify at Senate Armed Services Committee hearing .