Stress.

A school recently spent £3,600 on private detectives to follow a woman teacher off work through stress.
My sympathies are with the school. Stress is one of those areas - like vague backache - which is totally unprovable. (I speak as one suffering that latter kind of pain myself, currently.)
I have encountered this situation  on a number of occasions and 'stress' magically kicks in when somebody is facing disciplinary action.
The hands of the employer are then tied. Trade unions or professional organisations then take the alleged victim's side and legal action is threatened.
Once again - as someone who has suffered genuine stress myself and solved it without detriment to my employers, my sympathies go with those who act honestly.
The worst thing in the world would be to persecute a victim of genuine stress.
What is truly bad is when you have to rely on the honesty of someone whose honesty you doubt.