Silent Hill 1 back in '99 as a kid is the most scared I've been by a video game in my whole life. the entire atmosphere, music, psychological elements, the disturbing monsters, fog and the entire tone of the game was unlike anything I'd played by that point and I cut my horror teeth on RE1-3, AITD so I had played horror games prior.
as an adult Visage is probably the most scared I've been. the problem is that the game felt overly obtuse, largely boring and just lacked at hitting all the notes I love about horror games. that said I haven't had many games make me take "fear breaks" but hoo boy did that game make me take some of those lol.