Yup, you got the rules exacly right.

Hydrocodone is normally known by many because of its use as a painkiller but it also suppresses cough. It's a CNS depressant also.

Combined that with THC which can be a CNS depressant and you can have no interaction, increased drowiness all the way up to becoming quite stoned from both. Some people don't like it or can't handle it others have no problem. It depends on tolerance of both, body weight, amount consumed, etc. as well as the fact that you're probably sick.

Start low go slow.