Sorry not to sound sympathetic however this sounds very strange. These kind of arguments/altercations between travellers and airport staff happen every day, at every airport around the world. I travel, say, 20+ times a year all over the world and I either experience or witness similar incidents to your's multiple times each trip. You just have to watch one of those UK airline shows on TV to see people get into screaming matches with each other.
To want to cancel your trip and want to visit a GP because of this sounds nothing short of bizarre to me. You are either extremely mentally fragile or some key detail of this story is missing.
Screaming match! I am glad that I live in Perh. During my time in the UK never once I witnessed such a thing like a screaming match at the airport. The TV show about the airport is a TV show. It would have been boring if they show you the normal interactions. It is not the norm neither it should be to have screaming match at airports whether it is at Heathrow or Perth.
What one sees as bizarre, other might see as normal. I am not mentally fragile, and Singapore Airlines should respond to customers' complaints so that at least the other side of the story is known. But to put false statement on the computer system and say that I did not board voluntarily is bizarre.