Could this have been a sleep-related thing, or something else?

Experiences around the edge of sleep can feel startlingly real. The brain can produce sensations of pressure, a presence in the room, or changes in how the room seems while you are drifting off or waking up. Sleep paralysis is one possibility, though it usually involves being unable to move, which you did not mention. One episode by itself does not establish what caused it.

If it happens again, note whether you were falling asleep or waking, how long it lasted, and whether you could move and breathe normally. If the sensations happen while fully awake, keep recurring, or come with significant pain or breathing trouble, check in with a healthcare professional.

I would start with the ordinary checks: room temperature, bedding, airflow, and whether you were tense or overtired. Fear can make normal sensations feel more threatening, and shivering can follow a surge of anxiety or feeling cold. That does not mean the sensations were made up. It just gives you a few grounded possibilities before jumping to a paranormal explanation.

The dream is unsettling, but it is not proof that your partner somehow knew the secret. Dreams can combine familiar people and themes in unexpected ways, and a striking match can feel especially meaningful after the fact. You could ask what details they remember and when they first told you, without assuming it points to anything supernatural.