Inna in innī provides emphasis; the attached first-person pronoun is its noun. The lām in la-amḍī adds further emphasis. Amḍī, a first-person singular imperfect from m-ḍ-y, is used here for driving a worry away or moving past it.
ʿInda iḥtiḍārihi indicates when distress presents itself. The pronoun -hi refers back to al-hamm, not to the she-camel. Treating anxiety as if it arrives in person gives an abstract emotion a vivid presence.