This is the 1665th most frequent Japanese word.
襲っ
"襲っ" means "to attack" or "to assault."
Here, 襲われる (osowareru) is used in the passive form to denote being attacked or overwhelmed by a feeling (anxiety in this case).
彼は突然買い物中に不安感に襲われました。
He was suddenly overcome with anxiety while shopping.
In this sentence, 襲われる (osowareru) indicates being struck or affected by a sudden and intense event (heavy rain here).
森の中で大雨に襲われた。
We were caught in a heavy rainfall in the forest.
Here, 襲う (osou) is used actively, describing the action of attacking performed by the wild beast.