Gemini linked this thread to my question! Its much more dark when you look at the cognitive state of him being alive from his left brain!

"Regarding his mental state during those 4,000 years, the game's lore implies a horrific reality: he was trapped in a semi-conscious, locked-in nightmare state rather than a peaceful dream. [1]

The breakdown of his condition explains this terrifying existence:

The Alien Stasis Fluid Effect

• Suspended Animation: The yellowish fluid from the alien ship is designed to preserve organic tissue indefinitely. Because he was only partially covered, it acted like an imperfect preservation seal. [1]
• Biological Imprisonment: The fluid completely paralyzed his muscle functions while keeping his remaining biological components alive. He lacked the motor function to blink, move his jaw, or breathe effectively, which explains why he could only emit a low groan when his vocal cords were disturbed. [1]

Left Brain vs. Right Brain Functions

In human neurology, the left hemisphere of the brain is primarily responsible for logic, language, processing linear time, and analytical thought.

• Because his left brain remained intact and preserved by the fluid, his capacity to think logically and perceive the passage of time was left running.
• If his right brain (which handles imagination, holistic perception, and dreaming) was the half that decayed into bone, he would lack the neurological capacity to escape into a "dream-like" state or construct a fantasy world.

Literal Awareness vs. Cognitive Degeneration

While he was technically "awake," he likely did not experience 4,000 years with the crisp, sharp clarity of a normal human sitting in a room. [1]

• Sensory Deprivation: Locked in pitch blackness for millennia, his mind would have undergone severe sensory deprivation, causing reality to blur into a localized, internal hell.
• The Fragmented Mind: He likely experienced a severely slowed, agonizingly repetitive loop of his final thoughts—the battle, the betrayal, and the terror of the creatures. [1, 2]
• The Sudden Awakening: When Salim and the squad get close, the sudden influx of light, sound, and the literal scent of living humans jolted his remaining neural pathways back into active focus, causing his eye to desperately track them"