mine started doing this a few years ago and it led to a 6month + feeding strike, he wouldnt take anything no matter how hard i tried, he eventually ate and kept eating for another year, then went on a second 6month strike, now hes fine though. unfortunatly when it was happening i had no access to any information on what to do, so i kept everything the same and he eventually started eating, i hope this doesnt happen to you though.

try leaving a f/t over night with him in his usual enclosure and see if that helps