Today we would call it burn-out. It is a common problem among clergy, though in some other faiths, but rarely in Judaism, there is the further, more drastic problem of clergy drop-out for religious or intellectual reasons.
For rabbis, the problem is not likely to be Judaism but the congregation. It may be a congregation that resists the Jewish commitment for which the rabbi would give his life.
There may be an expectation gap: the rabbi wants to be a teacher of Torah and the congregation see him as a functionary, fundraiser, promoter, salesman and entertainer.
The rabbi may have agonies of conscience, far from happy at having to turn a blind eye (or two) to the moral and ethical compromises of some of his members.
There may be a problem of freedom of the pulpit: how can a rabbi give fearless leadership to the people who control his contract?
(A London rabbi who served his congregation for seven years once said that in his first year he was idolised, in the second he was patronised, in the third criticised, in the fourth terrorised, in the fifth scandalised, in the sixth ostracised, and in the seventh demobilised!)
It is a lonely occupation: a rabbi may have many friends but will find few soul-mates. The hours are long, the work is sensitive, there is a strain on one’s nervous system and one’s wife and family pay a price.
There is no rabbi who does not have moments of sheer fatigue and frustration, but fortunately most bounce back and assure themselves, as Moses must surely have done, that theirs is the most worthwhile job in the world.