There can be an emotional component to Tramadol... the first time I took it, I had mild hallucinations... just jumbled thinking.
I didn't sleep at all that night, and recall our late kitty Tippy sleeping right on me the whole time. When I rolled over, or got up for the bathroom she's jump right back on when I returned!
She never did that before at home, but sometimes on vacation, for some reason. Cats I have learned have some psychic traits, and this is one time, it reinforced by feelings about them.

The itching has to do with the serotonin actions. Opiates also can cause itching. Codeine is also activated in the liver, so it is slow to act. Oxycodone and buprenorphine are sometimes used for treatment resistant depressions too. They seem to affect serotonin in the brain for some people. There are a couple of threads on NT at our bipolar forum and Depression forum discussing this.

Each person has his/her own unique serotonin levels-- some high already and others lower. The high serotonin types don't like SSRI antidepressants and often react to some opiates.

There is a general observation about the itching. Those who itch with natural opiates, like codeine and morphine, don't usually complain about the synthetic ones, like oxycodone. And the reverse also happens with other patients. Patients often call this an "allergy", but it is not really most of the time. It is a serotonin effect, and metabolic.