Tramadol works on ascending pathways in the spine. The transmitter it blocks is similar to those blocked by antidepressents, but it is not centrally acting in this respect. In a small number of patients it is metabolised to a substance that works on opiate receptors in the brain, and this gives rise to the confusion.
It means that the drug may have far more analgesic effect on one patient than another, and may be morphine sparing in some and not in others.
From a flying perspective, convertors may be elated and have other morphine like side effects so it is a no no. It is also a no no (clinically at least0 because it can produce depression. And after about 10 weeks of use you can get non dependency withdrawal effects.
IMHO it is a great drug short term if you dont get too many side effects, but for most people poorly tolerated long term if they are working