I have also noticed him standing around with his thumb up his bottom completely failing to heal me as my HP plummets. And it's not because he's on CD; all his abilities are available, but there he stands doing nothing. I haven't figured out what provokes it or any common thread in when it happens.
Doc Lag... yeah.. that's what it is. Doc Lag. He will heal.. but first you must chomp some dirt so that he knows he is lagging and needs to get with he program.
And to the member who necro'ed Doc and his personal problems.. I applaud that you actually use search.
Just learn to check dates before poping the coffin lid.