Thank you Omegalamed. I did speak to the child psychology professional on the phone today and she was not all concerned! She said that there is no evidence to suggest he has a psychological issue that is at the root it this. He is an otherwise happy and sociable child. Rather, he knows that talking in this manner upsets me, so he used that as a means to express his anger and to try to get what he wants. He didn't get what he wants, which was to get the snorkel back, so hopefully I have reinforced that it is not acceptable to use that language to get what he wants.

I am so relieved! Behaviour management and boundary setting I can work with over time. I'm just immensely relieved it's not an indication of something more serious.

I definitely will also be working towards a reduction of time spent on video games.

I edited to add that my son and I did talk last night about the incident, and the reason why he said "I'll just drown myself then," was because he was worried he would drown in the pool without the snorkel, which he has been using, which adds another dimension to the incident. No wonder he was angry!