Facebook is a habit-forming activity - but users who spend a lot of time on the site say they feel less happy with their lives.
University of Gothenburg researchers say that many users log in as soon as they turn their PCs on - and that the behaviour can develop into an 'addiction'.
People in low income groups and the poorly educated are particularly at risk.
Up to 85% of users say that they use Facebook daily - and half say they start up Facebook as soon as they open their web users.
Half fear that they are not 'on top of things' if they are not logged into the site, and 25% say they fill 'ill at ease' if they can't log in regularly.
The Swedish survey, which polled 1,000 people aged 18-73 showed the network had its dark side.
'Facebooking may become an unconscious habit. A majority of the respondents log in every time they start their web browser. This may even develop into an addiction,' says Leif Denti, doctoral student of Psychology at the University of Gothenburg.
People with low income and low-educated individuals spend more time on Facebook.
Women are generally more active than men on Facebook.
