Hi annemollie, I disagree with the suggestion that there should be a comma after 'According to'. As DTcrossword fan says, the comma should be after the brackets.
According to Welch (2008, p336), patients' fears may arise from ...............
Well I don't agree there should be anything after the brackets BUT the contents of the bracket is a separate clause and you should still be able to write the sentence without it - in your case that wouldn't make sense:
According to patients' fears may arise from...
I'd leave out the brackets
Yes prudie, the (2008, p.336) is the reference to Welch's particular publication, which will be listed in full detail in ILB's references at the back of her piece of work.