You have a plushie in the room that you can squeeze to raise your sanity meter- which you can see lowering on the right of your screen. If it depletes, Ari catches you, so keep squeezing the plushie.
If you already are doing this, be aware that sometimes the Sanity meter rapidly drains out of nowhere, like when Misty knocks at the left door- you basically have to spend most of your time in the office squeezing the plushie every night, only opening cameras once Misty has attacked and an error needs fixing.