In one sense, it doesn't matter if it's a real memory or not. It's affecting K the same way a memory would.

K describes a particularly horrible iteration of dreams Jesus himself has had: being alone and trapped, moved around with no way to move himself. Being completely at the mercy of indifferent forces he could never hope to stop. And given what he knows about K... He'd be surprised if someone as compassionate as K didn't have those fears.

It doesn't make it any less terrible.

"You've had that dream before you came here?"