I keep seeing / imagining things that aren't there

[izzywinnf]

Occasionally i will imagine something for example, words on a wall or an object that is not there. It looks completely real. I then focus and double check and it completely vanishes like it wasn't there.

I thought it could be due to lack of sleep and tiredness but i also experience it when i have had normal amounts of sleep.

For example, today i saw a girl carrying a large WHITE  'art' type folder down the street, when i looked properly the girl was still there but she didn't have a folder she just had a BLACK handbag. It really confused me how i could possibly have imagined / thought she had a folder when she did not have this at all.

My vision is very good and i can see well both long and short distance. I am not sure why i keep seeing these things that are not actually there.

Has anyone else experience this or, not what it might be?

Thanks !!