Definition
To experience hallucinations or to imagine things that are not actually present.
I didn't sleep well last night, and I started to think I saw the walls moving; I must have been seeing things.
When I was walking alone on the dark road, I thought I saw someone following me, but I guess I was just seeing things.
He has been under too much pressure at work lately and has started seeing strange visions; he should see a doctor to confirm if he's seeing things.