why does walt have a downwards spiral in season 3?

after his meeting wth gus in Kafkaesque why does walt go into a downwards spiral?

instantly after his meeting he attempts to kill himself on the road and later on the whole fly episode. was it because he realised after the meeting that gus might kill him after the deal. or is it because of his loss of control, i feel like its implicated from gus extending the offer.