Walking Shadows (2002)

Suffering from depression following a traumatic psychedelic drug trip, college sophomore Elliot attempts to re-acclimate himself to his friends while scaling back on his excessive lifestyle. Then his self-control falters, his relationships to girlfriend Alli and close friend Madeline grow more confusing, and Elliot begins to grow paranoid that a dangerous man is stalking him from the shadows. Elliot's fears appear confirmed when his friends start disappearing, but he is unable to determine the difference between coincidences reinforced by his altered perception and increased anxiety, or a genuine threat that he's powerless to stop.