Entrepreneur (Via Business Opportunities Weblog): “How can you tell if a lack of human interaction is putting a crimp in your style? Some typical indications of being overly isolated are irritability, loss of energy and sadness unrelated to an identifiable cause.”
Even sitting in a room with other people it can sometimes seem quite isolated especially if the room is darkened to facilitate better color perception. I remember reading of experiments in the 1960’s where people voluntarily climbed into immersion tanks and floated in complete darkness for hours at a time with no physical contact.