That dosage of Oxycodone would be inappropriate for a cat, although I've seen that your cat is actually 6ft tall, so nix what I just said.
In all seriousness though, we don't use the nom de guerre system of trying to conceal your indentity. It's not a big deal at all, we just don't like to use it, as it can cause a great deal of confusion with people. It's just much easier to say I. In this day and age, if the government wanted a piece of you, they'd be watching you 24/7 through your webcam. They'd know your full name, your friends' names, what kind of girls your like and everything in between. It's just not a practice that does anybody any good. Even as draconian as our government is toward our kind, they're not interested in prosecuting us.
Sedating antihistamines shouldn't contribute significantly to respiratory depression, which would be the most dangerous possiblity in most cases of Opioid overdose. It will increase your subjective level of sedation, but it won't contribute to causing you to overdose. I enjoy taking antihistamines with my Opioids for the enhanced sedation. More power to you.