Is it possible to be in love with someone you no nothing about?

There is this guy that works in the same building as I who I have known for 6 years. I only see him at work and have only talked to him in ping. (there are 400 people employed where i work). For the last 5 months I've been in contact withhim mor than the norm and lately I can't seem to ge him off my mind. I feel ill if I do't get a chance to speak to him or see him. Am I a nut case or am I in love with him?