Are you in the USA? Most other countries, security would not carry a pistol, so perhaps they feel you can still do your job?
The fact that they want you working days instead may be a sign they are trying to work wkth you to find a solution but don’t feel firing you is warranted.
Do you want to be fired? If security is not for you, you’d be better served finding a different job and continuing to work days until you find something else that hopefully you like and is better for your mental health. Even working days rather than nights may be helpful.
Please don’t take this the wrong way, but as someone who doesn’t work security nor janitorial, I’d think of a janitor as a harder worker worth better hours and needing more training/experience. Security is often better paid but more dangerous, with unsociable hours, hence the pay. Your comment made it sound like you think yourself better. However, I presume you intended it as just that you can’t complete security tasks.