This happened to me as a kid. Must have been about 8 or 9. Was spending a late night with dad browsing the internet. Went down a rabbit hole watching optical illusions on some random website.

One illusion was to stare at a painting in a photo. Dad got bored and looked away. As he does that a face pops up on the screen and screams. Everything has been silent until then. The speakers were on full blast.

Now have a thing for suspense and jumpscares to the point i have to google jump scares in a movie so im prepared before i watch it