As per the title - I'll try and give my personal and professional experience, without providing any specific medical advice (which is fraught with risk over the internet, without being familiar with your medical history).
I have been working as a specialist General Practitioner for the last 5 years, and am currently working in a COVID screening clinic in Melbourne seeing all the lovely coughs and colds.
What’s your opinion on people coming in asking for medical certificates for mental health days, without any physical ailment?