Games like SICK
Games like SICK include Layers of Fear (2016), SOMA, Little Nightmares II, Mouthwashing, and Little Nightmares. We matched them by the tags players give SICK on Steam (Adventure, Psychological Horror, Horror, Atmospheric, and Walking Simulator): closest matches first, and among equally close ones the better-known games.

Layers of Fear (2016)
Shared: Psychological Horror · Horror · Atmospheric

SOMA
Shared: Psychological Horror · Horror · Atmospheric

Little Nightmares II
Shared: Adventure · Horror · Psychological Horror

Mouthwashing
Shared: Psychological Horror · Horror · Atmospheric

Little Nightmares
Shared: Adventure · Horror · Atmospheric

Blair Witch
Shared: Adventure · Horror · Psychological Horror

Hellblade: Senua's Sacrifice
Shared: Atmospheric · Adventure · Horror

Firewatch
Shared: Adventure · Atmospheric · Walking Simulator

Darkwood
Shared: Adventure · Horror · Psychological Horror

Outlast
Shared: Horror · Psychological Horror · Atmospheric

What Remains of Edith Finch
Shared: Atmospheric · Walking Simulator · Adventure

Sally Face - Episode One
Shared: Psychological Horror · Horror · Adventure

Still Wakes the Deep
Shared: Psychological Horror · Horror · Walking Simulator

Visage
Shared: Psychological Horror · Horror · Dark

The Medium
Shared: Adventure · Horror · Psychological Horror

Layers of Fear 2 (2019)
Shared: Psychological Horror · Horror · Atmospheric

Amnesia: A Machine For Pigs
Shared: Horror · Walking Simulator · Atmospheric

Outlast 2
Shared: Psychological Horror · Horror · Atmospheric

Fran Bow
Shared: Psychological Horror · Adventure · Horror

[Chillas Art] The Convenience Store
Shared: Horror · Psychological Horror · Adventure

SILENT HILL 2
Shared: Psychological Horror · Horror · Atmospheric

Among the Sleep - Enhanced Edition
Shared: Horror · Adventure · Atmospheric

Detention
Shared: Horror · Psychological Horror · Atmospheric

DISTRAINT: Deluxe Edition
Shared: Psychological Horror · Horror · Adventure