Before coming to Hogwarts, many child witches and wizards display some sort of latent magical ability, by performing magic instinctively: e.g. Harry making his hair grow incredibly fast or making a pane of glass disappear, Neville bouncing when dropped from a window, etc. Such acts appear to be motivated only by the subconscious: Harry didn't want to have almost no hair, but didn't know he could do anything about it.
Does this sort of 'instinctive' magic manifest only in children?
Of course, adult witches and wizards have had training and so they're likely to know what kind of spell to use and be able to do so consciously. But say they can't: if an adult is in some life-threatening situation and doesn't know how to escape, is it possible for them to cast some instinctive non-verbal spell that they don't even understand in order to save themselves, as children can do so easily?