He said: "It could be because of pupil behaviour, because of workload, it could be because of things such as pressure for results. There could be bullying and harassment issues or it could be because of inspections.
"Some of the days lost that are not put down to stress may be stress related in some way, but people don't necessarily want to put stress down as a reason.
"In the more enlightened times that we're in now, we would like to think people would specify the true reason they're off but we do find for people who've been off for a long period of time, it might be stress but called something else."