I think, for me, the answer would be "sometimes," depending on the situation.
Possibly the most effective "startle" scene in cinema occurs in the original version of "The Exorcist." Father Karras is alone in a university basement listening to tape recordings of the possessed girl, Regan. He thinks he hears something in a dead space on one of the tapes. As he keeps playing this barely audible snippet over and over again, we, as the audience, are also straining, trying to hear what he hears. Thinking we might just be able to make it out, it has our full attention when...
...someone bursts through a door behind the priest and says "Hello!"
This illustrates a couple of features that I think can magnify the startle response - complete fixation on a task and hypersensitivity to sound. The film makes you hypersensitive to sound by getting you to drop all your defenses to loud noises in your effort to make out what's on the tape. It also makes you devote all your attention to the task of figuring out what you're listening to - then something loud comes out of left field.
Sound sensitivity is something that seems fairly common in ME. Fixation on a task may also be more common because the effects of "brain fog' may require an unusual amount of focus in order to accomplish some objective.
Just some thoughts...