I find that not many text-based horror games are able to unsettle me, but this was fantastic.
The small details were perfect (my favorite being the vocabulary words becoming more sinister over time), and it's a great function to have the player be able to keep checking the man outside- really increased my paranoia. The multitasking between "keeping watch" and the vocabulary minigame really enhances both aspects. And of course, the sound design is perfectly subtle in all the right places. It's a breath of fresh air to see horror done well without cheap tricks or irritating tropes.
Please do keep creating horror stuff like this, you're a very skilled storyteller!