Chuck is able to slowly change his mental state.
He begins in a normal mental state, however goes through many of the different mental illnesses. Many factors cause Chuck to become depressed. Whenever Chuck looks at the locket with the picture of Kelly, he feels alone and longs to see her. At times he feels hopeless as isolation closes in. Chuck fears he will never get off the island and will never see his Kelly again. Thankfully, "Wilson" helps him cope with his feelings of anxiety and mood swings. Many times when he is talking to "Wilson" about their situation, Chuck experiences mood swings. For example, when Chuck is in the cave talking to"Wilson" about his plan to get off the island he gets very angry and expresses it by throwing "Wilson" out of the cave. Within a matter of seconds he begins to call out for "Wilson" and runs out of the cave
to find him as he experiences a feeling of loss and loneliness. During the course of four years we learn that Chuck considered suicide as an option which shows the amount of pain he experienced during his attacks of mood swings and anxiety. Chuck also experienced psychosis where his rational thoughts and perceptions were severely imparied. Often he would experience a psychotic episode involving a loss of contact with reality. This can be seen as he begins to actually talk and rationalize with a volley ball. Chuck would talk to "Wilson" believing at times the ball would answer back. He felt such a bond with this ball, truly believing this was a real human individual causing a psychosis moment for Chuck when he loses "Wilson" causing him to break down crying.