Deep Sleep is a series of point-and-click adventure games created by Polish indie developer Mateusz Sokalszczuk (also known by his online name scriptwelder).

The series consists of three free browser games in which the player attempts to navigate and eventually escape a dream world inhabited by shadow people.

A dark room in a long hallway contains multiple news clippings informing the researcher of mysterious events that imply he's far from the only one to have ventured into this nightmare realm.

Following the events of the previous game, the protagonist develops an obsession over the previously-encountered shadow people, and begins to worry that they may be real entities.

A torn book page, slowly reassembled over the course of the game, give more insight into the nature of the Shadow People, which are described as ancient otherworldly entities that exist only in the dream world and desire to escape into the real world by possessing the uninhabited bodies of people stuck in comas or lucid dreams.

They explain that the protagonist is a fool for returning and informs him that he has descended too far down to re-ascend like last time, and must hit the bottom in order to "bounce" back to the waking realm.

Picking up at a different point in time from the previous game, the player awakens in their bed, immobile, and sees a shadowy figure in their room, which briefly attacks before vanishing.

Upon escaping the sewer system, the player enters a room explored in a previous game, where they discover that their uninhabited body had become possessed when they descended into the well, and they are now a Shadow Person themselves.

Adam Smith of Rock, Paper, Shotgun wrote that although the game has a minimalist story, it "relies on mood rather than jump scares to unsettle".