What depressed me more than anything about lockdown was people's blatant disregard and even pride about disobeying all rules. People saying the pandemic is a hoax and laughing at people listening to expert bodies as they quote their friend from the pool hall or a Facebook meme.
I think all rational thought goes out of the window in the throes of a bout of anxiety or a panic attack. We are convinced that the worst is about to happen and it never does, yet we're still convinced. It's really odd.
My best friend died in a fight when he was 16 (I was 15). I went off the rails for a long time after that. I believe his death to be the root cause of my depression (many years later). You're right, major trigger.