Pediococcus can make a beer viscous like that, but "the sickness" supposedly clears up after a while and the beer becomes more pleasant to drink. I've never experienced it though, so I don't have first hand knowledge. I think Vinnie Cilurzo said that he spoke with some Belgian lambic brewers. One said that the sickness was key to his best batches of lambic. The other said when his beers got sick he dumped them. So it should be obvious by now, right?