User blog comment:Theory of everything/Is Nick loosing his Grimm powers?/@comment-1509826-20120422112549/@comment-2255188-20120422185116

That's a good point-- Nick probably is subconsciously thinking, "I wonder if they're a Wesen," when he confronts people, causing himself to subconsciously reveal his Grimmness...which in turn frightens the Wesen and causes them to reveal themselves. So with that in mind, Nick probably wouldn't have approached the nurse the same way he approaches most strangers.