One of the more annoying differences in Trakenite physiology is how much sleep his body needs; nearly ten Gallifreyan hours if he's going to be at his mental and physical peak. Discipline can reduce the need over the short term, but his ability to focus plummets after only a day or two.
Worse than that are the dreams; instead of remembering things as they happened, his sleeping mind conjures up alternative scenarios.
The bad ones are horrible enough, but at least waking from them is a relief. Feeling the pleasant ones slip away as he awakens is the true torment.