烦乱 specifically describes inner emotional/mental turmoil — the mind is
烦 (vexed) and
乱 (in disorder). Distinguish from
烦躁 (fánzào, restless and irritable),
心烦 (xīnfán, vexed), and
慌乱 (huāngluàn, panicky and disordered).
烦乱 is more often written than spoken.