I have the same problem, I used to have trouble sleeping when I first was on hydrocodone, but now that I have been on it so many years, I just get pain relief and dont notice anything else.
When my pain flairs, a couple of times a year, my doctor will switch my hydrocodone with oxycodone, and then I have the same problem. I will feel tired, but cant sleep. I assume this will go away if you are on it for any length of time.
I know people who take oxycodone and ambian, but you shouldnt accept that kind of advice from a message board, if you arent 100% sure, call your pharmacist, or your doctor, before mixing any meds.
Good luck and please post and let us know what you find out.
Your Friend, Fabby