One of the most common misreadings of tazkiyah is to measure it by how a person feels right now. Calm is taken as progress; a heavy chest is taken as regression.
But mood is a passing state, shaped by sleep, food, pressure and the people around us. Tazkiyah is long work on what a person wants, intends and is willing to persist in. The two sometimes coincide, and sometimes part company for a long while.
Confusing them is costly. It leaves a person chasing a feeling instead of building a habit, and reading every difficulty as a punishment — which on its own is enough to make the difficulty last longer.