Can the company fire you for having a flashback at work

I am not clear on what you mean by having a flashback. If this was something to do with your mental or physical health, it may amount to discrimination based on your disability or perceived disability contrary to your human rights. Employers are able to terminate your employment not for cause by providing you with reasonable notice or payment in lieu of reasonable notice, so long as it is not based on discriminatory reasons. I would recommend that you reach out to an employment lawyer.