Desiria

I'm on mac osx 10.6.8...avatar wouldn't walk, jerky, suddenly...on SL viewer. What could it be?  Been workin absolutely fine for week, then suddenly flew to another part of the site, and rezzing slowed way down, and my avatar felt frozen, jerky, wouldn't walk, couldn't type in IM or box.... words appeared after, and gear spinning on my computer. Help please? Is this normal at times, or something I have to adjust in my prefs? Prefer good advice for mac osx 10.6.8 if anyone knows.......thanks.