Welcome to the forum! :)
Drug companies are required to list all possible side effects, even if only one person out of millions reported it. They don't want to get sued so they cover their butts. I can pretty much assure you that 20mg is not a big enough dose to cause any harm to you. You probably will experience some side effects — but those will go away once you get used to the medication (within the first week or two).
If you're still concerned, check out this page (scroll down) to see a table of side effects and how often they occur for people with anxiety disorders.www.rxlist.com/paxil-side-effects-drug-center.htm
It seems as though the most common symptoms for anxiety disorder sufferers are nausea, dry mouth, and GI problems. (Also take note that the "placebo" group reported many of the same issues!)