A friend of mine who works as a professional pilot in GA also had this happen recently.
Some incredibly gutless and vexatious person reported him to CASA as having suicidal tendencies and so forth. CASA wouldn't reveal who made the report citing confidentiality. The onus (and cost) was on him to prove that he wasn't unfit to fly as accused by this anonymous waste of oxygen, and his medical was suspended until this could be done by visiting specialists.
The accusations were of course completely baseless. No presumption of innocence. Mind you, what else would expect from our regulator?
On another related note; I had my medical renewal recently. My DAME highlighted to me out all the new post-German wings questioning around mental health. He is of the opinion that the tougher stance will only serve to drive pilots who actually have mental health issues to conceal them further.