The Oxygen meter definitely adds a bit of needed challenge and conceptually makes the whole thing darker since you're literally suffocating beneath a mask of emotion. I like the narrative detail when you pass out that they wait for you to wake up before getting rid of you.
Is there any way to "win" the game? It might be interesting to have another activity for you to try to get a "win" ending, and you have to stop doing that activity and put on your mask when the emotions show up. Mechanically this other activity could just be spamming a button 400 times or something, whatever seem doable. (You could say the character is trying to radio off-planet, or build an escape route, or pray to a passing asteroid full of ghosts, etc, anything that fits your story/concept.) You could also make oxygen run out faster if you try to do the action while wearing a mask (adding risk/reward), and make emotions catch you faster if you do it a few times while not wearing a mask. Just a thought!
I kinda want a "suspicion" bar filling up when emotions are present, just to add some panic to putting the mask on in time. Not super necessary though.
Also: It's great to know about Project HTMLifier, thanks for mentioning it!